Java SE > Java SE Specifications > Java Virtual Machine Specification
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A Java Virtual Machine instruction consists of an opcode specifying the operation to be performed, followed by zero or more operands embodying values to be operated upon. This chapter gives details about the format of each Java Virtual Machine instruction and the operation it performs.
The description of each instruction is always given in the context of Java Virtual Machine code that satisfies the static and structural constraints of §4 (The class File Format). In the description of individual Java Virtual Machine instructions, we frequently state that some situation "must" or "must not" be the case: "The value2 must be of type int." The constraints of §4 (The class File Format) guarantee that all such expectations will in fact be met. If some constraint (a "must" or "must not") in an instruction description is not satisfied at run time, the behavior of the Java Virtual Machine is undefined.
The Java Virtual Machine checks that Java Virtual Machine code satisfies the static and structural constraints at link time using a class file verifier (§4.10). Thus, a Java Virtual Machine will only attempt to execute code from valid class files. Performing verification at link time is attractive in that the checks are performed just once, substantially reducing the amount of work that must be done at run time. Other implementation strategies are possible, provided that they comply with The Java Language Specification, Java SE 15 Edition and The Java Virtual Machine Specification, Java SE 15 Edition.
In addition to the opcodes of the instructions specified later in this chapter, which are used in class files (§4 (The class File Format)), three opcodes are reserved for internal use by a Java Virtual Machine implementation. If the instruction set of the Java Virtual Machine is extended in the future, these reserved opcodes are guaranteed not to be used.
Two of the reserved opcodes, numbers 254 (0xfe) and 255 (0xff), have the mnemonics impdep1 and impdep2, respectively. These instructions are intended to provide "back doors" or traps to implementation-specific functionality implemented in software and hardware, respectively. The third reserved opcode, number 202 (0xca), has the mnemonic breakpoint and is intended to be used by debuggers to implement breakpoints.
Although these opcodes have been reserved, they may be used only inside a Java Virtual Machine implementation. They cannot appear in valid class files. Tools such as debuggers or JIT code generators (§2.13) that might directly interact with Java Virtual Machine code that has been already loaded and executed may encounter these opcodes. Such tools should attempt to behave gracefully if they encounter any of these reserved instructions.
A Java Virtual Machine implementation throws an object that is an instance of a subclass of the class VirtualMachineError when an internal error or resource limitation prevents it from implementing the semantics described in this chapter. This specification cannot predict where internal errors or resource limitations may be encountered and does not mandate precisely when they can be reported. Thus, any of the VirtualMachineError subclasses defined below may be thrown at any time during the operation of the Java Virtual Machine:
InternalError: An internal error has occurred in the Java Virtual Machine implementation because of a fault in the software implementing the virtual machine, a fault in the underlying host system software, or a fault in the hardware. This error is delivered asynchronously (§2.10) when it is detected and may occur at any point in a program.
OutOfMemoryError: The Java Virtual Machine implementation has run out of either virtual or physical memory, and the automatic storage manager was unable to reclaim enough memory to satisfy an object creation request.
StackOverflowError: The Java Virtual Machine implementation has run out of stack space for a thread, typically because the thread is doing an unbounded number of recursive invocations as a result of a fault in the executing program.
UnknownError: An exception or error has occurred, but the Java Virtual Machine implementation is unable to report the actual exception or error.
Java Virtual Machine instructions are represented in this chapter by entries of the form shown below, in alphabetical order and each beginning on a new page.
A longer description detailing constraints on operand stack contents or constant pool entries, the operation performed, the type of the results, etc.
If any linking exceptions may be thrown by the execution of this instruction, they are set off one to a line, in the order in which they must be thrown.
If any run-time exceptions can be thrown by the execution of an instruction, they are set off one to a line, in the order in which they must be thrown.
Other than the linking and run-time exceptions, if any, listed for an instruction, that instruction must not throw any run-time exceptions except for instances of VirtualMachineError or its subclasses.
Each cell in the instruction format diagram represents a single 8-bit byte. The instruction's mnemonic is its name. Its opcode is its numeric representation and is given in both decimal and hexadecimal forms. Only the numeric representation is actually present in the Java Virtual Machine code in a class file.
Keep in mind that there are "operands" generated at compile time and embedded within Java Virtual Machine instructions, as well as "operands" calculated at run time and supplied on the operand stack. Although they are supplied from several different areas, all these operands represent the same thing: values to be operated upon by the Java Virtual Machine instruction being executed. By implicitly taking many of its operands from its operand stack, rather than representing them explicitly in its compiled code as additional operand bytes, register numbers, etc., the Java Virtual Machine's code stays compact.
Some instructions are presented as members of a family of related instructions sharing a single description, format, and operand stack diagram. As such, a family of instructions includes several opcodes and opcode mnemonics; only the family mnemonic appears in the instruction format diagram, and a separate forms line lists all member mnemonics and opcodes. For example, the Forms line for the lconst_<l> family of instructions, giving mnemonic and opcode information for the two instructions in that family (lconst_0 and lconst_1), is
In the description of the Java Virtual Machine instructions, the effect of an instruction's execution on the operand stack (§2.6.2) of the current frame (§2.6) is represented textually, with the stack growing from left to right and each value represented separately. Thus,
shows an operation that begins by having value2 on top of the operand stack with value1 just beneath it. As a result of the execution of the instruction, value1 and value2 are popped from the operand stack and replaced by result value, which has been calculated by the instruction. The remainder of the operand stack, represented by an ellipsis (...), is unaffected by the instruction's execution.
Values of types long and double are represented by a single entry on the operand stack.
In the First Edition of The Java® Virtual Machine Specification, values on the operand stack of types long and double were each represented in the stack diagram by two entries.
The arrayref must be of type reference and must refer to an array whose components are of type reference. The index must be of type int. Both arrayref and index are popped from the operand stack. The reference value in the component of the array at index is retrieved and pushed onto the operand stack.
The arrayref must be of type reference and must refer to an array whose components are of type reference. The index must be of type int, and value must be of type reference. The arrayref, index, and value are popped from the operand stack.
If value is null, then value is stored as the component of the array at index.
Otherwise, value is non-null. If the type of value is assignment compatible with the type of the components of the array referenced by arrayref, then value is stored as the component of the array at index.
The following rules are used to determine whether a value that is not null is assignment compatible with the array component type. If S is the type of the object referred to by value, and T is the reference type of the array components, then aastore determines whether assignment is compatible as follows:
If arrayref is null, aastore throws a NullPointerException.
Otherwise, if index is not within the bounds of the array referenced by arrayref, the aastore instruction throws an ArrayIndexOutOfBoundsException.
Otherwise, if arrayref is not null and the actual type of the non-null value is not assignment compatible with the actual type of the components of the array, aastore throws an ArrayStoreException.
The index is an unsigned byte that must be an index into the local variable array of the current frame (§2.6). The local variable at index must contain a reference. The objectref in the local variable at index is pushed onto the operand stack.
The aload instruction cannot be used to load a value of type returnAddress from a local variable onto the operand stack. This asymmetry with the astore instruction (§astore) is intentional.
The aload opcode can be used in conjunction with the wide instruction (§wide) to access a local variable using a two-byte unsigned index.
The <n> must be an index into the local variable array of the current frame (§2.6). The local variable at <n> must contain a reference. The objectref in the local variable at <n> is pushed onto the operand stack.
An aload_<n> instruction cannot be used to load a value of type returnAddress from a local variable onto the operand stack. This asymmetry with the corresponding astore_<n> instruction (§astore_<n>) is intentional.
Each of the aload_<n> instructions is the same as aload with an index of <n>, except that the operand <n> is implicit.
The count must be of type int. It is popped off the operand stack. The count represents the number of components of the array to be created. The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class (§2.6), where the value of the index is (indexbyte1 << 8) | indexbyte2. The run-time constant pool entry at the index must be a symbolic reference to a class, array, or interface type. The named class, array, or interface type is resolved (§5.4.3.1). A new array with components of that type, of length count, is allocated from the garbage-collected heap, and a reference arrayref to this new array object is pushed onto the operand stack. All components of the new array are initialized to null, the default value for reference types (§2.4).
During resolution of the symbolic reference to the class, array, or interface type, any of the exceptions documented in §5.4.3.1 can be thrown.
The objectref must be of type reference and must refer to an object of a type that is assignment compatible (JLS §5.2) with the type represented by the return descriptor (§4.3.3) of the current method. If the current method is a synchronized method, the monitor entered or reentered on invocation of the method is updated and possibly exited as if by execution of a monitorexit instruction (§monitorexit) in the current thread. If no exception is thrown, objectref is popped from the operand stack of the current frame (§2.6) and pushed onto the operand stack of the frame of the invoker. Any other values on the operand stack of the current method are discarded.
The interpreter then reinstates the frame of the invoker and returns control to the invoker.
If the Java Virtual Machine implementation does not enforce the rules on structured locking described in §2.11.10, then if the current method is a synchronized method and the current thread is not the owner of the monitor entered or reentered on invocation of the method, areturn throws an IllegalMonitorStateException. This can happen, for example, if a synchronized method contains a monitorexit instruction, but no monitorenter instruction, on the object on which the method is synchronized.
Otherwise, if the Java Virtual Machine implementation enforces the rules on structured locking described in §2.11.10 and if the first of those rules is violated during invocation of the current method, then areturn throws an IllegalMonitorStateException.
The index is an unsigned byte that must be an index into the local variable array of the current frame (§2.6). The objectref on the top of the operand stack must be of type returnAddress or of type reference. It is popped from the operand stack, and the value of the local variable at index is set to objectref.
The astore instruction is used with an objectref of type returnAddress when implementing the finally clause of the Java programming language (§3.13).
The aload instruction (§aload) cannot be used to load a value of type returnAddress from a local variable onto the operand stack. This asymmetry with the astore instruction is intentional.
The astore opcode can be used in conjunction with the wide instruction (§wide) to access a local variable using a two-byte unsigned index.
The <n> must be an index into the local variable array of the current frame (§2.6). The objectref on the top of the operand stack must be of type returnAddress or of type reference. It is popped from the operand stack, and the value of the local variable at <n> is set to objectref.
An astore_<n> instruction is used with an objectref of type returnAddress when implementing the finally clauses of the Java programming language (§3.13).
An aload_<n> instruction (§aload_<n>) cannot be used to load a value of type returnAddress from a local variable onto the operand stack. This asymmetry with the corresponding astore_<n> instruction is intentional.
Each of the astore_<n> instructions is the same as astore with an index of <n>, except that the operand <n> is implicit.
The objectref must be of type reference and must refer to an object that is an instance of class Throwable or of a subclass of Throwable. It is popped from the operand stack. The objectref is then thrown by searching the current method (§2.6) for the first exception handler that matches the class of objectref, as given by the algorithm in §2.10.
If an exception handler that matches objectref is found, it contains the location of the code intended to handle this exception. The pc register is reset to that location, the operand stack of the current frame is cleared, objectref is pushed back onto the operand stack, and execution continues.
If no matching exception handler is found in the current frame, that frame is popped. If the current frame represents an invocation of a synchronized method, the monitor entered or reentered on invocation of the method is exited as if by execution of a monitorexit instruction (§monitorexit). Finally, the frame of its invoker is reinstated, if such a frame exists, and the objectref is rethrown. If no such frame exists, the current thread exits.
If objectref is null, athrow throws a NullPointerException instead of objectref.
Otherwise, if the Java Virtual Machine implementation does not enforce the rules on structured locking described in §2.11.10, then if the method of the current frame is a synchronized method and the current thread is not the owner of the monitor entered or reentered on invocation of the method, athrow throws an IllegalMonitorStateException instead of the object previously being thrown. This can happen, for example, if an abruptly completing synchronized method contains a monitorexit instruction, but no monitorenter instruction, on the object on which the method is synchronized.
Otherwise, if the Java Virtual Machine implementation enforces the rules on structured locking described in §2.11.10 and if the first of those rules is violated during invocation of the current method, then athrow throws an IllegalMonitorStateException instead of the object previously being thrown.
The operand stack diagram for the athrow instruction may be misleading: If a handler for this exception is matched in the current method, the athrow instruction discards all the values on the operand stack, then pushes the thrown object onto the operand stack. However, if no handler is matched in the current method and the exception is thrown farther up the method invocation chain, then the operand stack of the method (if any) that handles the exception is cleared and objectref is pushed onto that empty operand stack. All intervening frames from the method that threw the exception up to, but not including, the method that handles the exception are discarded.
The arrayref must be of type reference and must refer to an array whose components are of type byte or of type boolean. The index must be of type int. Both arrayref and index are popped from the operand stack. The byte value in the component of the array at index is retrieved, sign-extended to an int value, and pushed onto the top of the operand stack.
If arrayref is null, baload throws a NullPointerException.
Otherwise, if index is not within the bounds of the array referenced by arrayref, the baload instruction throws an ArrayIndexOutOfBoundsException.
The baload instruction is used to load values from both byte and boolean arrays. In Oracle's Java Virtual Machine implementation, boolean arrays - that is, arrays of type T_BOOLEAN (§2.2, §newarray) - are implemented as arrays of 8-bit values. Other implementations may implement packed boolean arrays; the baload instruction of such implementations must be used to access those arrays.
The arrayref must be of type reference and must refer to an array whose components are of type byte or of type boolean. The index and the value must both be of type int. The arrayref, index, and value are popped from the operand stack.
If the arrayref refers to an array whose components are of type byte, then the int value is truncated to a byte and stored as the component of the array indexed by index.
If the arrayref refers to an array whose components are of type boolean, then the int value is narrowed by taking the bitwise AND of value and 1; the result is stored as the component of the array indexed by index.
If arrayref is null, bastore throws a NullPointerException.
Otherwise, if index is not within the bounds of the array referenced by arrayref, the bastore instruction throws an ArrayIndexOutOfBoundsException.
The bastore instruction is used to store values into both byte and boolean arrays. In Oracle's Java Virtual Machine implementation, boolean arrays - that is, arrays of type T_BOOLEAN (§2.2, §newarray) - are implemented as arrays of 8-bit values. Other implementations may implement packed boolean arrays; in such implementations the bastore instruction must be able to store boolean values into packed boolean arrays as well as byte values into byte arrays.
The arrayref must be of type reference and must refer to an array whose components are of type char. The index must be of type int. Both arrayref and index are popped from the operand stack. The component of the array at index is retrieved and zero-extended to an int value. That value is pushed onto the operand stack.
The arrayref must be of type reference and must refer to an array whose components are of type char. The index and the value must both be of type int. The arrayref, index, and value are popped from the operand stack. The int value is truncated to a char and stored as the component of the array indexed by index.
The objectref must be of type reference. The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class (§2.6), where the value of the index is (indexbyte1 << 8) | indexbyte2. The run-time constant pool entry at the index must be a symbolic reference to a class, array, or interface type.
If objectref is null, then the operand stack is unchanged.
Otherwise, the named class, array, or interface type is resolved (§5.4.3.1). If objectref can be cast to the resolved class, array, or interface type, the operand stack is unchanged; otherwise, the checkcast instruction throws a ClassCastException.
The following rules are used to determine whether an objectref that is not null can be cast to the resolved type. If S is the type of the object referred to by objectref, and T is the resolved class, array, or interface type, then checkcast determines whether objectref can be cast to type T as follows:
During resolution of the symbolic reference to the class, array, or interface type, any of the exceptions documented in §5.4.3.1 can be thrown.
Otherwise, if objectref cannot be cast to the resolved class, array, or interface type, the checkcast instruction throws a ClassCastException.
The checkcast instruction is very similar to the instanceof instruction (§instanceof). It differs in its treatment of null, its behavior when its test fails (checkcast throws an exception, instanceof pushes a result code), and its effect on the operand stack.
The value on the top of the operand stack must be of type double. It is popped from the operand stack and undergoes value set conversion (§2.8.3) resulting in value'. Then value' is converted to a float result using the round to nearest rounding policy (§2.8). The result is pushed onto the operand stack.
Where an d2f instruction is FP-strict (§2.8.2), the result of the conversion is always rounded to the nearest representable value in the float value set (§2.3.2).
Where an d2f instruction is not FP-strict, the result of the conversion may be taken from the float-extended-exponent value set (§2.3.2); it is not necessarily rounded to the nearest representable value in the float value set.
A finite value' too small to be represented as a float is converted to a zero of the same sign; a finite value' too large to be represented as a float is converted to an infinity of the same sign. A double NaN is converted to a float NaN.
The value on the top of the operand stack must be of type double. It is popped from the operand stack and undergoes value set conversion (§2.8.3) resulting in value'. Then value' is converted to an int result. The result is pushed onto the operand stack:
If the value' is NaN, the result of the conversion is an int 0.
Otherwise, if the value' is not an infinity, it is rounded to an integer value V using the round toward zero rounding policy (§2.8). If this integer value V can be represented as an int, then the result is the int value V.
Otherwise, either the value' must be too small (a negative value of large magnitude or negative infinity), and the result is the smallest representable value of type int, or the value' must be too large (a positive value of large magnitude or positive infinity), and the result is the largest representable value of type int.
The value on the top of the operand stack must be of type double. It is popped from the operand stack and undergoes value set conversion (§2.8.3) resulting in value'. Then value' is converted to a long. The result is pushed onto the operand stack:
If the value' is NaN, the result of the conversion is a long 0.
Otherwise, if the value' is not an infinity, it is rounded to an integer value V using the round toward zero rounding policy (§2.8). If this integer value V can be represented as a long, then the result is the long value V.
Otherwise, either the value' must be too small (a negative value of large magnitude or negative infinity), and the result is the smallest representable value of type long, or the value' must be too large (a positive value of large magnitude or positive infinity), and the result is the largest representable value of type long.
Both value1 and value2 must be of type double. The values are popped from the operand stack and undergo value set conversion (§2.8.3), resulting in value1' and value2'. The double result is value1' + value2'. The result is pushed onto the operand stack.
The result of a dadd instruction is governed by the rules of IEEE 754 arithmetic:
The sum of two infinities of the same sign is the infinity of that sign.
The sum of an infinity and any finite value is equal to the infinity.
The sum of two zeroes of the same sign is the zero of that sign.
The sum of a zero and a nonzero finite value is equal to the nonzero value.
The sum of two nonzero finite values of the same magnitude and opposite sign is positive zero.
In the remaining cases, where neither operand is an infinity, a zero, or NaN and the values have the same sign or have different magnitudes, the sum is computed and rounded to the nearest representable value using the round to nearest rounding policy (§2.8). If the magnitude is too large to represent as adouble, we say the operation overflows; the result is then an infinity of appropriate sign. If the magnitude is too small to represent as a double, we say the operation underflows; the result is then a zero of appropriate sign.
The Java Virtual Machine requires support of gradual underflow. Despite the fact that overflow, underflow, or loss of precision may occur, execution of a dadd instruction never throws a run-time exception.
The arrayref must be of type reference and must refer to an array whose components are of type double. The index must be of type int, and value must be of type double. The arrayref, index, and value are popped from the operand stack. The double value undergoes value set conversion (§2.8.3), resulting in value', which is stored as the component of the array indexed by index.
Both value1 and value2 must be of type double. The values are popped from the operand stack and undergo value set conversion (§2.8.3), resulting in value1' and value2'. A floating-point comparison is performed:
If value1' is greater than value2', the int value 1 is pushed onto the operand stack.
Otherwise, if value1' is equal to value2', the int value 0 is pushed onto the operand stack.
Otherwise, if value1' is less than value2', the int value -1 is pushed onto the operand stack.
Otherwise, at least one of value1' or value2' is NaN. The dcmpg instruction pushes the int value 1 onto the operand stack and the dcmpl instruction pushes the int value -1 onto the operand stack.
Floating-point comparison is performed in accordance with IEEE 754. All values other than NaN are ordered, with negative infinity less than all finite values and positive infinity greater than all finite values. Positive zero and negative zero are considered equal.
The dcmpg and dcmpl instructions differ only in their treatment of a comparison involving NaN. NaN is unordered, so any double comparison fails if either or both of its operands are NaN. With both dcmpg and dcmpl available, any double comparison may be compiled to push the same result onto the operand stack whether the comparison fails on non-NaN values or fails because it encountered a NaN. For more information, see §3.5.
Both value1 and value2 must be of type double. The values are popped from the operand stack and undergo value set conversion (§2.8.3), resulting in value1' and value2'. The double result is value1' / value2'. The result is pushed onto the operand stack.
The result of a ddiv instruction is governed by the rules of IEEE 754 arithmetic:
If neither value1' nor value2' is NaN, the sign of the result is positive if both values have the same sign, negative if the values have different signs.
Division of an infinity by a finite value results in a signed infinity, with the sign-producing rule just given.
Division of a finite value by an infinity results in a signed zero, with the sign-producing rule just given.
Division of a zero by a zero results in NaN; division of zero by any other finite value results in a signed zero, with the sign-producing rule just given.
Division of a nonzero finite value by a zero results in a signed infinity, with the sign-producing rule just given.
In the remaining cases, where neither operand is an infinity, a zero, or NaN, the quotient is computed and rounded to the nearest double using the round to nearest rounding policy (§2.8). If the magnitude is too large to represent as a double, we say the operation overflows; the result is then an infinity of appropriate sign. If the magnitude is too small to represent as a double, we say the operation underflows; the result is then a zero of appropriate sign.
The Java Virtual Machine requires support of gradual underflow. Despite the fact that overflow, underflow, division by zero, or loss of precision may occur, execution of a ddiv instruction never throws a run-time exception.
The index is an unsigned byte. Both index and index+1 must be indices into the local variable array of the current frame (§2.6). The local variable at index must contain a double. The value of the local variable at index is pushed onto the operand stack.
The dload opcode can be used in conjunction with the wide instruction (§wide) to access a local variable using a two-byte unsigned index.
Both <n> and <n>+1 must be indices into the local variable array of the current frame (§2.6). The local variable at <n> must contain a double. The value of the local variable at <n> is pushed onto the operand stack.
Both value1 and value2 must be of type double. The values are popped from the operand stack and undergo value set conversion (§2.8.3), resulting in value1' and value2'. The double result is value1' * value2'. The result is pushed onto the operand stack.
The result of a dmul instruction is governed by the rules of IEEE 754 arithmetic:
If neither value1' nor value2' is NaN, the sign of the result is positive if both values have the same sign and negative if the values have different signs.
Multiplication of an infinity by a finite value results in a signed infinity, with the sign-producing rule just given.
In the remaining cases, where neither an infinity nor NaN is involved, the product is computed and rounded to the nearest representable value using the round to nearest rounding policy (§2.8). If the magnitude is too large to represent as a double, we say the operation overflows; the result is then an infinity of appropriate sign. If the magnitude is too small to represent as a double, we say the operation underflows; the result is then a zero of appropriate sign.
The Java Virtual Machine requires support of gradual underflow. Despite the fact that overflow, underflow, or loss of precision may occur, execution of a dmul instruction never throws a run-time exception.
The value must be of type double. It is popped from the operand stack and undergoes value set conversion (§2.8.3), resulting in value'. The double result is the arithmetic negation of value'. The result is pushed onto the operand stack.
For double values, negation is not the same as subtraction from zero. If x is +0.0, then 0.0-x equals +0.0, but -x equals -0.0. Unary minus merely inverts the sign of a double.
Both value1 and value2 must be of type double. The values are popped from the operand stack and undergo value set conversion (§2.8.3), resulting in value1' and value2'. The double result is calculated and pushed onto the operand stack.
The result of a drem instruction is not the same as the result of the remainder operation defined by IEEE 754, due to the choice of rounding policy in the Java Virtual Machine (§2.8). The IEEE 754 remainder operation computes the remainder from a rounding division, not a truncating division, and so its behavior is not analogous to that of the usual integer remainder operator. Instead, the Java Virtual Machine defines drem to behave in a manner analogous to that of the integer remainder instructions irem and lrem, with an implied division using the round toward zero rounding policy; this may be compared with the C library function fmod.
The result of a drem instruction is governed by the following rules, which match IEEE 754 arithmetic except for how the implied division is computed:
If neither value1' nor value2' is NaN, the sign of the result equals the sign of the dividend.
If the dividend is an infinity or the divisor is a zero or both, the result is NaN.
If the dividend is finite and the divisor is an infinity, the result equals the dividend.
If the dividend is a zero and the divisor is finite, the result equals the dividend.
In the remaining cases, where neither operand is an infinity, a zero, or NaN, the floating-point remainder result from a dividend value1' and a divisor value2' is defined by the mathematical relation result = value1' - (value2' * q), where q is an integer that is negative only if value1' / value2' is negative, and positive only if value1' / value2' is positive, and whose magnitude is as large as possible without exceeding the magnitude of the true mathematical quotient of value1' and value2'.
Despite the fact that division by zero may occur, evaluation of a drem instruction never throws a run-time exception. Overflow, underflow, or loss of precision cannot occur.
The current method must have return type double. The value must be of type double. If the current method is a synchronized method, the monitor entered or reentered on invocation of the method is updated and possibly exited as if by execution of a monitorexit instruction (§monitorexit) in the current thread. If no exception is thrown, value is popped from the operand stack of the current frame (§2.6) and undergoes value set conversion (§2.8.3), resulting in value'. The value' is pushed onto the operand stack of the frame of the invoker. Any other values on the operand stack of the current method are discarded.
The interpreter then returns control to the invoker of the method, reinstating the frame of the invoker.
If the Java Virtual Machine implementation does not enforce the rules on structured locking described in §2.11.10, then if the current method is a synchronized method and the current thread is not the owner of the monitor entered or reentered on invocation of the method, dreturn throws an IllegalMonitorStateException. This can happen, for example, if a synchronized method contains a monitorexit instruction, but no monitorenter instruction, on the object on which the method is synchronized.
Otherwise, if the Java Virtual Machine implementation enforces the rules on structured locking described in §2.11.10 and if the first of those rules is violated during invocation of the current method, then dreturn throws an IllegalMonitorStateException.
The index is an unsigned byte. Both index and index+1 must be indices into the local variable array of the current frame (§2.6). The value on the top of the operand stack must be of type double. It is popped from the operand stack and undergoes value set conversion (§2.8.3), resulting in value'. The local variables at index and index+1 are set to value'.
The dstore opcode can be used in conjunction with the wide instruction (§wide) to access a local variable using a two-byte unsigned index.
Both <n> and <n>+1 must be indices into the local variable array of the current frame (§2.6). The value on the top of the operand stack must be of type double. It is popped from the operand stack and undergoes value set conversion (§2.8.3), resulting in value'. The local variables at <n> and <n>+1 are set to value'.
Both value1 and value2 must be of type double. The values are popped from the operand stack and undergo value set conversion (§2.8.3), resulting in value1' and value2'. The double result is value1' - value2'. The result is pushed onto the operand stack.
For double subtraction, it is always the case that a-b produces the same result as a+(-b). However, for the dsub instruction, subtraction from zero is not the same as negation, because if x is +0.0, then 0.0-x equals +0.0, but -x equals -0.0.
The Java Virtual Machine requires support of gradual underflow. Despite the fact that overflow, underflow, or loss of precision may occur, execution of a dsub instruction never throws a run-time exception.
Duplicate the top value on the operand stack and push the duplicated value onto the operand stack.
The dup instruction must not be used unless value is a value of a category 1 computational type (§2.11.1).
Duplicate the top value on the operand stack and insert the duplicated value two values down in the operand stack.
The dup_x1 instruction must not be used unless both value1 and value2 are values of a category 1 computational type (§2.11.1).
Duplicate the top one or two operand stack values and insert two, three, or four values down
..., value4, value3, value2, value1 →
..., value2, value1, value4, value3, value2, value1
where value1, value2, value3, and value4 are all values of a category 1 computational type (§2.11.1).
..., value1, value3, value2, value1
where value1 is a value of a category 2 computational type and value2 and value3 are both values of a category 1 computational type (§2.11.1).
..., value2, value1, value3, value2, value1
where value1 and value2 are both values of a category 1 computational type and value3 is a value of a category 2 computational type (§2.11.1).
where value1 and value2 are both values of a category 2 computational type (§2.11.1).
The value on the top of the operand stack must be of type float. It is popped from the operand stack and undergoes value set conversion (§2.8.3), resulting in value'. Then value' is converted to a double result. This result is pushed onto the operand stack.
Where an f2d instruction is FP-strict (§2.8.2) it performs a widening primitive conversion (JLS §5.1.2). Because all values of the float value set (§2.3.2) are exactly representable by values of the double value set (§2.3.2), such a conversion is exact.
Where an f2d instruction is not FP-strict, the result of the conversion may be taken from the double-extended-exponent value set; it is not necessarily rounded to the nearest representable value in the double value set. However, if the operand value is taken from the float-extended-exponent value set and the target result is constrained to the double value set, rounding of value may be required.
The value on the top of the operand stack must be of type float. It is popped from the operand stack and undergoes value set conversion (§2.8.3), resulting in value'. Then value' is converted to an int result. This result is pushed onto the operand stack:
If the value' is NaN, the result of the conversion is an int 0.
Otherwise, if the value' is not an infinity, it is rounded to an integer value V using the round toward zero rounding policy (§2.8). If this integer value V can be represented as an int, then the result is the int value V.
Otherwise, either the value' must be too small (a negative value of large magnitude or negative infinity), and the result is the smallest representable value of type int, or the value' must be too large (a positive value of large magnitude or positive infinity), and the result is the largest representable value of type int.
The value on the top of the operand stack must be of type float. It is popped from the operand stack and undergoes value set conversion (§2.8.3), resulting in value'. Then value' is converted to a long result. This result is pushed onto the operand stack:
If the value' is NaN, the result of the conversion is a long 0.
Otherwise, if the value' is not an infinity, it is rounded to an integer value V using the round toward zero rounding policy (§2.8). If this integer value V can be represented as a long, then the result is the long value V.
Otherwise, either the value' must be too small (a negative value of large magnitude or negative infinity), and the result is the smallest representable value of type long, or the value' must be too large (a positive value of large magnitude or positive infinity), and the result is the largest representable value of type long.
Both value1 and value2 must be of type float. The values are popped from the operand stack and undergo value set conversion (§2.8.3), resulting in value1' and value2'. The float result is value1' + value2'. The result is pushed onto the operand stack.
The result of an fadd instruction is governed by the rules of IEEE 754 arithmetic:
The sum of two infinities of the same sign is the infinity of that sign.
The sum of an infinity and any finite value is equal to the infinity.
The sum of two zeroes of the same sign is the zero of that sign.
The sum of a zero and a nonzero finite value is equal to the nonzero value.
The sum of two nonzero finite values of the same magnitude and opposite sign is positive zero.
In the remaining cases, where neither operand is an infinity, a zero, or NaN and the values have the same sign or have different magnitudes, the sum is computed and rounded to the nearest representable value using the round to nearest rounding policy (§2.8). If the magnitude is too large to represent as a float, we say the operation overflows; the result is then an infinity of appropriate sign. If the magnitude is too small to represent as a float, we say the operation underflows; the result is then a zero of appropriate sign.
The Java Virtual Machine requires support of gradual underflow. Despite the fact that overflow, underflow, or loss of precision may occur, execution of an fadd instruction never throws a run-time exception.
The arrayref must be of type reference and must refer to an array whose components are of type float. The index must be of type int, and the value must be of type float. The arrayref, index, and value are popped from the operand stack. The float value undergoes value set conversion (§2.8.3), resulting in value', and value' is stored as the component of the array indexed by index.
Both value1 and value2 must be of type float. The values are popped from the operand stack and undergo value set conversion (§2.8.3), resulting in value1' and value2'. A floating-point comparison is performed:
If value1' is greater than value2', the int value 1 is pushed onto the operand stack.
Otherwise, if value1' is equal to value2', the int value 0 is pushed onto the operand stack.
Otherwise, if value1' is less than value2', the int value -1 is pushed onto the operand stack.
Otherwise, at least one of value1' or value2' is NaN. The fcmpg instruction pushes the int value 1 onto the operand stack and the fcmpl instruction pushes the int value -1 onto the operand stack.
Floating-point comparison is performed in accordance with IEEE 754. All values other than NaN are ordered, with negative infinity less than all finite values and positive infinity greater than all finite values. Positive zero and negative zero are considered equal.
The fcmpg and fcmpl instructions differ only in their treatment of a comparison involving NaN. NaN is unordered, so any float comparison fails if either or both of its operands are NaN. With both fcmpg and fcmpl available, any float comparison may be compiled to push the same result onto the operand stack whether the comparison fails on non-NaN values or fails because it encountered a NaN. For more information, see §3.5.
Both value1 and value2 must be of type float. The values are popped from the operand stack and undergo value set conversion (§2.8.3), resulting in value1' and value2'. The float result is value1' / value2'. The result is pushed onto the operand stack.
The result of an fdiv instruction is governed by the rules of IEEE 754 arithmetic:
If neither value1' nor value2' is NaN, the sign of the result is positive if both values have the same sign, negative if the values have different signs.
Division of an infinity by a finite value results in a signed infinity, with the sign-producing rule just given.
Division of a finite value by an infinity results in a signed zero, with the sign-producing rule just given.
Division of a zero by a zero results in NaN; division of zero by any other finite value results in a signed zero, with the sign-producing rule just given.
Division of a nonzero finite value by a zero results in a signed infinity, with the sign-producing rule just given.
In the remaining cases, where neither operand is an infinity, a zero, or NaN, the quotient is computed and rounded to the nearest float using the round to nearest rounding policy (§2.8). If the magnitude is too large to represent as a float, we say the operation overflows; the result is then an infinity of appropriate sign. If the magnitude is too small to represent as a float, we say the operation underflows; the result is then a zero of appropriate sign.
The Java Virtual Machine requires support of gradual underflow. Despite the fact that overflow, underflow, division by zero, or loss of precision may occur, execution of an fdiv instruction never throws a run-time exception.
The index is an unsigned byte that must be an index into the local variable array of the current frame (§2.6). The local variable at index must contain a float. The value of the local variable at index is pushed onto the operand stack.
The fload opcode can be used in conjunction with the wide instruction (§wide) to access a local variable using a two-byte unsigned index.
The <n> must be an index into the local variable array of the current frame (§2.6). The local variable at <n> must contain a float. The value of the local variable at <n> is pushed onto the operand stack.
Both value1 and value2 must be of type float. The values are popped from the operand stack and undergo value set conversion (§2.8.3), resulting in value1' and value2'. The float result is value1' * value2'. The result is pushed onto the operand stack.
The result of an fmul instruction is governed by the rules of IEEE 754 arithmetic:
If neither value1' nor value2' is NaN, the sign of the result is positive if both values have the same sign, and negative if the values have different signs.
Multiplication of an infinity by a finite value results in a signed infinity, with the sign-producing rule just given.
In the remaining cases, where neither an infinity nor NaN is involved, the product is computed and rounded to the nearest representable value using the round to nearest rounding policy (§2.8). If the magnitude is too large to represent as a float, we say the operation overflows; the result is then an infinity of appropriate sign. If the magnitude is too small to represent as a float, we say the operation underflows; the result is then a zero of appropriate sign.
The Java Virtual Machine requires support of gradual underflow. Despite the fact that overflow, underflow, or loss of precision may occur, execution of an fmul instruction never throws a run-time exception.
The value must be of type float. It is popped from the operand stack and undergoes value set conversion (§2.8.3), resulting in value'. The float result is the arithmetic negation of value'. This result is pushed onto the operand stack.
For float values, negation is not the same as subtraction from zero. If x is +0.0, then 0.0-x equals +0.0, but -x equals -0.0. Unary minus merely inverts the sign of a float.
Both value1 and value2 must be of type float. The values are popped from the operand stack and undergo value set conversion (§2.8.3), resulting in value1' and value2'. The float result is calculated and pushed onto the operand stack.
The result of an frem instruction is not the same as the result of the remainder operation defined by IEEE 754, due to the choice of rounding policy in the Java Virtual Machine (§2.8). The IEEE 754 remainder operation computes the remainder from a rounding division, not a truncating division, and so its behavior is not analogous to that of the usual integer remainder operator. Instead, the Java Virtual Machine defines frem to behave in a manner analogous to that of the integer remainder instructions irem and lrem, with an implied division using the round toward zero rounding policy; this may be compared with the C library function fmod.
The result of an frem instruction is governed by the following rules, which match IEEE 754 arithmetic except for how the implied division is computed:
If neither value1' nor value2' is NaN, the sign of the result equals the sign of the dividend.
If the dividend is an infinity or the divisor is a zero or both, the result is NaN.
If the dividend is finite and the divisor is an infinity, the result equals the dividend.
If the dividend is a zero and the divisor is finite, the result equals the dividend.
In the remaining cases, where neither operand is an infinity, a zero, or NaN, the floating-point remainder result from a dividend value1' and a divisor value2' is defined by the mathematical relation result = value1' - (value2' * q), where q is an integer that is negative only if value1' / value2' is negative and positive only if value1' / value2' is positive, and whose magnitude is as large as possible without exceeding the magnitude of the true mathematical quotient of value1' and value2'.
Despite the fact that division by zero may occur, evaluation of an frem instruction never throws a run-time exception. Overflow, underflow, or loss of precision cannot occur.
The current method must have return type float. The value must be of type float. If the current method is a synchronized method, the monitor entered or reentered on invocation of the method is updated and possibly exited as if by execution of a monitorexit instruction (§monitorexit) in the current thread. If no exception is thrown, value is popped from the operand stack of the current frame (§2.6) and undergoes value set conversion (§2.8.3), resulting in value'. The value' is pushed onto the operand stack of the frame of the invoker. Any other values on the operand stack of the current method are discarded.
The interpreter then returns control to the invoker of the method, reinstating the frame of the invoker.
If the Java Virtual Machine implementation does not enforce the rules on structured locking described in §2.11.10, then if the current method is a synchronized method and the current thread is not the owner of the monitor entered or reentered on invocation of the method, freturn throws an IllegalMonitorStateException. This can happen, for example, if a synchronized method contains a monitorexit instruction, but no monitorenter instruction, on the object on which the method is synchronized.
Otherwise, if the Java Virtual Machine implementation enforces the rules on structured locking described in §2.11.10 and if the first of those rules is violated during invocation of the current method, then freturn throws an IllegalMonitorStateException.
The index is an unsigned byte that must be an index into the local variable array of the current frame (§2.6). The value on the top of the operand stack must be of type float. It is popped from the operand stack and undergoes value set conversion (§2.8.3), resulting in value'. The value of the local variable at index is set to value'.
The fstore opcode can be used in conjunction with the wide instruction (§wide) to access a local variable using a two-byte unsigned index.
The <n> must be an index into the local variable array of the current frame (§2.6). The value on the top of the operand stack must be of type float. It is popped from the operand stack and undergoes value set conversion (§2.8.3), resulting in value'. The value of the local variable at <n> is set to value'.
Both value1 and value2 must be of type float. The values are popped from the operand stack and undergo value set conversion (§2.8.3), resulting in value1' and value2'. The float result is value1' - value2'. The result is pushed onto the operand stack.
For float subtraction, it is always the case that a-b produces the same result as a+(-b). However, for the fsub instruction, subtraction from zero is not the same as negation, because if x is +0.0, then 0.0-x equals +0.0, but -x equals -0.0.
The Java Virtual Machine requires support of gradual underflow. Despite the fact that overflow, underflow, or loss of precision may occur, execution of an fsub instruction never throws a run-time exception.
The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class (§2.6), where the value of the index is (indexbyte1 << 8) | indexbyte2. The run-time constant pool entry at the index must be a symbolic reference to a field (§5.1), which gives the name and descriptor of the field as well as a symbolic reference to the class in which the field is to be found. The referenced field is resolved (§5.4.3.2).
The objectref, which must be of type reference but not an array type, is popped from the operand stack. The value of the referenced field in objectref is fetched and pushed onto the operand stack.
During resolution of the symbolic reference to the field, any of the errors pertaining to field resolution (§5.4.3.2) can be thrown.
Otherwise, if the resolved field is a static field, getfield throws an IncompatibleClassChangeError.
The getfield instruction cannot be used to access the length field of an array. The arraylength instruction (§arraylength) is used instead.
The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class (§2.6), where the value of the index is (indexbyte1 << 8) | indexbyte2. The run-time constant pool entry at the index must be a symbolic reference to a field (§5.1), which gives the name and descriptor of the field as well as a symbolic reference to the class or interface in which the field is to be found. The referenced field is resolved (§5.4.3.2).
On successful resolution of the field, the class or interface that declared the resolved field is initialized if that class or interface has not already been initialized (§5.5).
The value of the class or interface field is fetched and pushed onto the operand stack.
During resolution of the symbolic reference to the class or interface field, any of the exceptions pertaining to field resolution (§5.4.3.2) can be thrown.
Otherwise, if the resolved field is not a static (class) field or an interface field, getstatic throws an IncompatibleClassChangeError.
Otherwise, if execution of this getstatic instruction causes initialization of the referenced class or interface, getstatic may throw an Error as detailed in §5.5.
The unsigned bytes branchbyte1 and branchbyte2 are used to construct a signed 16-bit branchoffset, where branchoffset is (branchbyte1 << 8) | branchbyte2. Execution proceeds at that offset from the address of the opcode of this goto instruction. The target address must be that of an opcode of an instruction within the method that contains this goto instruction.
The unsigned bytes branchbyte1, branchbyte2, branchbyte3, and branchbyte4 are used to construct a signed 32-bit branchoffset, where branchoffset is (branchbyte1 << 24) | (branchbyte2 << 16) | (branchbyte3 << 8) | branchbyte4. Execution proceeds at that offset from the address of the opcode of this goto_w instruction. The target address must be that of an opcode of an instruction within the method that contains this goto_w instruction.
Although the goto_w instruction takes a 4-byte branch offset, other factors limit the size of a method to 65535 bytes (§4.11). This limit may be raised in a future release of the Java Virtual Machine.
The value on the top of the operand stack must be of type int. It is popped from the operand stack and converted to the float result using the round to nearest rounding policy (§2.8). The result is pushed onto the operand stack.
Both value1 and value2 must be of type int. The values are popped from the operand stack. The int result is value1 + value2. The result is pushed onto the operand stack.
The result is the 32 low-order bits of the true mathematical result in a sufficiently wide two's-complement format, represented as a value of type int. If overflow occurs, then the sign of the result may not be the same as the sign of the mathematical sum of the two values.
Despite the fact that overflow may occur, execution of an iadd instruction never throws a run-time exception.
iconst_m1 = 2 (0x2)
iconst_0 = 3 (0x3)
iconst_1 = 4 (0x4)
iconst_2 = 5 (0x5)
iconst_3 = 6 (0x6)
iconst_4 = 7 (0x7)
iconst_5 = 8 (0x8)
Both value1 and value2 must be of type int. The values are popped from the operand stack. The int result is the value of the Java programming language expression value1 / value2 (JLS §15.17.2). The result is pushed onto the operand stack.
An int division rounds towards 0; that is, the quotient produced for int values in n/d is an int value q whose magnitude is as large as possible while satisfying |d ⋅ q| ≤ |n|. Moreover, q is positive when |n| ≥ |d| and n and d have the same sign, but q is negative when |n| ≥ |d| and n and d have opposite signs.
There is one special case that does not satisfy this rule: if the dividend is the negative integer of largest possible magnitude for the int type, and the divisor is -1, then overflow occurs, and the result is equal to the dividend. Despite the overflow, no exception is thrown in this case.
Both value1 and value2 must be of type reference. They are both popped from the operand stack and compared. The results of the comparison are as follows:
If the comparison succeeds, the unsigned branchbyte1 and branchbyte2 are used to construct a signed 16-bit offset, where the offset is calculated to be (branchbyte1 << 8) | branchbyte2. Execution then proceeds at that offset from the address of the opcode of this if_acmp<cond> instruction. The target address must be that of an opcode of an instruction within the method that contains this if_acmp<cond> instruction.
Otherwise, if the comparison fails, execution proceeds at the address of the instruction following this if_acmp<cond> instruction.
if_icmpeq = 159 (0x9f)
if_icmpne = 160 (0xa0)
if_icmplt = 161 (0xa1)
if_icmpge = 162 (0xa2)
if_icmpgt = 163 (0xa3)
if_icmple = 164 (0xa4)
Both value1 and value2 must be of type int. They are both popped from the operand stack and compared. All comparisons are signed. The results of the comparison are as follows:
If the comparison succeeds, the unsigned branchbyte1 and branchbyte2 are used to construct a signed 16-bit offset, where the offset is calculated to be (branchbyte1 << 8) | branchbyte2. Execution then proceeds at that offset from the address of the opcode of this if_icmp<cond> instruction. The target address must be that of an opcode of an instruction within the method that contains this if_icmp<cond> instruction.
Otherwise, execution proceeds at the address of the instruction following this if_icmp<cond> instruction.
ifeq = 153 (0x99)
ifne = 154 (0x9a)
iflt = 155 (0x9b)
ifge = 156 (0x9c)
ifgt = 157 (0x9d)
ifle = 158 (0x9e)
The value must be of type int. It is popped from the operand stack and compared against zero. All comparisons are signed. The results of the comparisons are as follows:
If the comparison succeeds, the unsigned branchbyte1 and branchbyte2 are used to construct a signed 16-bit offset, where the offset is calculated to be (branchbyte1 << 8) | branchbyte2. Execution then proceeds at that offset from the address of the opcode of this if<cond> instruction. The target address must be that of an opcode of an instruction within the method that contains this if<cond> instruction.
Otherwise, execution proceeds at the address of the instruction following this if<cond> instruction.
The value must be of type reference. It is popped from the operand stack. If value is not null, the unsigned branchbyte1 and branchbyte2 are used to construct a signed 16-bit offset, where the offset is calculated to be (branchbyte1 << 8) | branchbyte2. Execution then proceeds at that offset from the address of the opcode of this ifnonnull instruction. The target address must be that of an opcode of an instruction within the method that contains this ifnonnull instruction.
Otherwise, execution proceeds at the address of the instruction following this ifnonnull instruction.
The value must of type reference. It is popped from the operand stack. If value is null, the unsigned branchbyte1 and branchbyte2 are used to construct a signed 16-bit offset, where the offset is calculated to be (branchbyte1 << 8) | branchbyte2. Execution then proceeds at that offset from the address of the opcode of this ifnull instruction. The target address must be that of an opcode of an instruction within the method that contains this ifnull instruction.
Otherwise, execution proceeds at the address of the instruction following this ifnull instruction.
The index is an unsigned byte that must be an index into the local variable array of the current frame (§2.6). The const is an immediate signed byte. The local variable at index must contain an int. The value const is first sign-extended to an int, and then the local variable at index is incremented by that amount.
The iinc opcode can be used in conjunction with the wide instruction (§wide) to access a local variable using a two-byte unsigned index and to increment it by a two-byte immediate signed value.
The index is an unsigned byte that must be an index into the local variable array of the current frame (§2.6). The local variable at index must contain an int. The value of the local variable at index is pushed onto the operand stack.
The iload opcode can be used in conjunction with the wide instruction (§wide) to access a local variable using a two-byte unsigned index.
The <n> must be an index into the local variable array of the current frame (§2.6). The local variable at <n> must contain an int. The value of the local variable at <n> is pushed onto the operand stack.
Both value1 and value2 must be of type int. The values are popped from the operand stack. The int result is value1 * value2. The result is pushed onto the operand stack.
The result is the 32 low-order bits of the true mathematical result in a sufficiently wide two's-complement format, represented as a value of type int. If overflow occurs, then the sign of the result may not be the same as the sign of the mathematical multiplication of the two values.
Despite the fact that overflow may occur, execution of an imul instruction never throws a run-time exception.
The value must be of type int. It is popped from the operand stack. The int result is the arithmetic negation of value, -value. The result is pushed onto the operand stack.
For int values, negation is the same as subtraction from zero. Because the Java Virtual Machine uses two's-complement representation for integers and the range of two's-complement values is not symmetric, the negation of the maximum negative int results in that same maximum negative number. Despite the fact that overflow has occurred, no exception is thrown.
The objectref, which must be of type reference, is popped from the operand stack. The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class (§2.6), where the value of the index is (indexbyte1 << 8) | indexbyte2. The run-time constant pool entry at the index must be a symbolic reference to a class, array, or interface type.
If objectref is null, the instanceof instruction pushes an int result of 0 as an int onto the operand stack.
Otherwise, the named class, array, or interface type is resolved (§5.4.3.1). If objectref is an instance of the resolved class or array type, or implements the resolved interface, the instanceof instruction pushes an int result of 1 as an int onto the operand stack; otherwise, it pushes an int result of 0.
The following rules are used to determine whether an objectref that is not null is an instance of the resolved type. If S is the type of the object referred to by objectref, and T is the resolved class, array, or interface type, then instanceof determines whether objectref is an instance of T as follows:
During resolution of the symbolic reference to the class, array, or interface type, any of the exceptions documented in §5.4.3.1 can be thrown.
The instanceof instruction is very similar to the checkcast instruction (§checkcast). It differs in its treatment of null, its behavior when its test fails (checkcast throws an exception, instanceof pushes a result code), and its effect on the operand stack.
First, the unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class (§2.6), where the value of the index is (indexbyte1 << 8) | indexbyte2. The run-time constant pool entry at the index must be a symbolic reference to a dynamically-computed call site (§5.1). The values of the third and fourth operand bytes must always be zero.
The symbolic reference is resolved (§5.4.3.6) for this specific invokedynamic instruction to obtain a reference to an instance of java.lang.invoke.CallSite. The instance of java.lang.invoke.CallSite is considered "bound" to this specific invokedynamic instruction.
The instance of java.lang.invoke.CallSite indicates a target method handle. The nargs argument values are popped from the operand stack, and the target method handle is invoked. The invocation occurs as if by execution of an invokevirtual instruction that indicates a run-time constant pool index to a symbolic reference R where:
and where it is as if the following items were pushed, in order, onto the operand stack:
During resolution of the symbolic reference to a dynamically-computed call site, any of the exceptions pertaining to dynamically-computed call site resolution can be thrown.
If the symbolic reference to the dynamically-computed call site can be resolved, it implies that a non-null reference to an instance of java.lang.invoke.CallSite is bound to the invokedynamic instruction. Therefore, the target method handle, indicated by the instance of java.lang.invoke.CallSite, is non-null.
Similarly, successful resolution implies that the method descriptor in the symbolic reference is semantically equal to the type descriptor of the target method handle.
Together, these invariants mean that an invokedynamic instruction which is bound to an instance of java.lang.invoke.CallSite never throws a NullPointerException or a java.lang.invoke.WrongMethodTypeException.
The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class (§2.6), where the value of the index is (indexbyte1 << 8) | indexbyte2. The run-time constant pool entry at the index must be a symbolic reference to an interface method (§5.1), which gives the name and descriptor (§4.3.3) of the interface method as well as a symbolic reference to the interface in which the interface method is to be found. The named interface method is resolved (§5.4.3.4).
The resolved interface method must not be an instance initialization method, or the class or interface initialization method (§2.9.1, §2.9.2).
The count operand is an unsigned byte that must not be zero. The objectref must be of type reference and must be followed on the operand stack by nargs argument values, where the number, type, and order of the values must be consistent with the descriptor of the resolved interface method. The value of the fourth operand byte must always be zero.
Let C be the class of objectref. A method is selected with respect to C and the resolved method (§5.4.6). This is the method to be invoked.
If the method to be invoked is synchronized, the monitor associated with objectref is entered or reentered as if by execution of a monitorenter instruction (§monitorenter) in the current thread.
If the method to be invoked is not native, the nargs argument values and objectref are popped from the operand stack. A new frame is created on the Java Virtual Machine stack for the method being invoked. The objectref and the argument values are consecutively made the values of local variables of the new frame, with objectref in local variable 0, arg1 in local variable 1 (or, if arg1 is of type long or double, in local variables 1 and 2), and so on. Any argument value that is of a floating-point type undergoes value set conversion (§2.8.3) prior to being stored in a local variable. The new frame is then made current, and the Java Virtual Machine pc is set to the opcode of the first instruction of the method to be invoked. Execution continues with the first instruction of the method.
If the method to be invoked is native and the platform-dependent code that implements it has not yet been bound (§5.6) into the Java Virtual Machine, then that is done. The nargs argument values and objectref are popped from the operand stack and are passed as parameters to the code that implements the method. Any argument value that is of a floating-point type undergoes value set conversion (§2.8.3) prior to being passed as a parameter. The parameters are passed and the code is invoked in an implementation-dependent manner. When the platform-dependent code returns:
If the native method is synchronized, the monitor associated with objectref is updated and possibly exited as if by execution of a monitorexit instruction (§monitorexit) in the current thread.
If the native method returns a value, the return value of the platform-dependent code is converted in an implementation-dependent way to the return type of the native method and pushed onto the operand stack.
During resolution of the symbolic reference to the interface method, any of the exceptions pertaining to interface method resolution (§5.4.3.4) can be thrown.
Otherwise, if the resolved method is static, the invokeinterface instruction throws an IncompatibleClassChangeError.
Note that invokeinterface may refer to private methods declared in interfaces, including nestmate interfaces.
Otherwise, if objectref is null, the invokeinterface instruction throws a NullPointerException.
Otherwise, if the class of objectref does not implement the resolved interface, invokeinterface throws an IncompatibleClassChangeError.
Otherwise, if the selected method is neither public nor private, invokeinterface throws an IllegalAccessError.
Otherwise, if the selected method is abstract, invokeinterface throws an AbstractMethodError.
Otherwise, if the selected method is native and the code that implements the method cannot be bound, invokeinterface throws an UnsatisfiedLinkError.
Otherwise, if no method is selected, and there are multiple maximally-specific superinterface methods of C that match the resolved method's name and descriptor and are not abstract, invokeinterface throws an IncompatibleClassChangeError
Otherwise, if no method is selected, and there are no maximally-specific superinterface methods of C that match the resolved method's name and descriptor and are not abstract, invokeinterface throws an AbstractMethodError.
The count operand of the invokeinterface instruction records a measure of the number of argument values, where an argument value of type long or type double contributes two units to the count value and an argument of any other type contributes one unit. This information can also be derived from the descriptor of the selected method. The redundancy is historical.
The fourth operand byte exists to reserve space for an additional operand used in certain of Oracle's Java Virtual Machine implementations, which replace the invokeinterface instruction by a specialized pseudo-instruction at run time. It must be retained for backwards compatibility.
The nargs argument values and objectref are not one-to-one with the first nargs+1 local variables. Argument values of types long and double must be stored in two consecutive local variables, thus more than nargs local variables may be required to pass nargs argument values to the invoked method.
The selection logic allows a non-abstract method declared in a superinterface to be selected. Methods in interfaces are only considered if there is no matching method in the class hierarchy. In the event that there are two non-abstract methods in the superinterface hierarchy, with neither more specific than the other, an error occurs; there is no attempt to disambiguate (for example, one may be the referenced method and one may be unrelated, but we do not prefer the referenced method). On the other hand, if there are many abstract methods but only one non-abstract method, the non-abstract method is selected (unless an abstract method is more specific).
Invoke instance method; direct invocation of instance initialization methods and methods of the current class and its supertypes
The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class (§2.6), where the value of the index is (indexbyte1 << 8) | indexbyte2. The run-time constant pool entry at the index must be a symbolic reference to a method or an interface method (§5.1), which gives the name and descriptor (§4.3.3) of the method or interface method as well as a symbolic reference to the class or interface in which the method or interface method is to be found. The named method is resolved (§5.4.3.3, §5.4.3.4).
If all of the following are true, let C be the direct superclass of the current class:
Otherwise, let C be the class or interface named by the symbolic reference.
The actual method to be invoked is selected by the following lookup procedure:
If C contains a declaration for an instance method with the same name and descriptor as the resolved method, then it is the method to be invoked.
Otherwise, if C is a class and has a superclass, a search for a declaration of an instance method with the same name and descriptor as the resolved method is performed, starting with the direct superclass of C and continuing with the direct superclass of that class, and so forth, until a match is found or no further superclasses exist. If a match is found, then it is the method to be invoked.
Otherwise, if C is an interface and the class Object contains a declaration of a public instance method with the same name and descriptor as the resolved method, then it is the method to be invoked.
Otherwise, if there is exactly one maximally-specific method (§5.4.3.3) in the superinterfaces of C that matches the resolved method's name and descriptor and is not abstract, then it is the method to be invoked.
The objectref must be of type reference and must be followed on the operand stack by nargs argument values, where the number, type, and order of the values must be consistent with the descriptor of the selected instance method.
If the method is synchronized, the monitor associated with objectref is entered or reentered as if by execution of a monitorenter instruction (§monitorenter) in the current thread.
If the method is not native, the nargs argument values and objectref are popped from the operand stack. A new frame is created on the Java Virtual Machine stack for the method being invoked. The objectref and the argument values are consecutively made the values of local variables of the new frame, with objectref in local variable 0, arg1 in local variable 1 (or, if arg1 is of type long or double, in local variables 1 and 2), and so on. Any argument value that is of a floating-point type undergoes value set conversion (§2.8.3) prior to being stored in a local variable. The new frame is then made current, and the Java Virtual Machine pc is set to the opcode of the first instruction of the method to be invoked. Execution continues with the first instruction of the method.
If the method is native and the platform-dependent code that implements it has not yet been bound (§5.6) into the Java Virtual Machine, that is done. The nargs argument values and objectref are popped from the operand stack and are passed as parameters to the code that implements the method. Any argument value that is of a floating-point type undergoes value set conversion (§2.8.3) prior to being passed as a parameter. The parameters are passed and the code is invoked in an implementation-dependent manner. When the platform-dependent code returns, the following take place:
If the native method is synchronized, the monitor associated with objectref is updated and possibly exited as if by execution of a monitorexit instruction (§monitorexit) in the current thread.
If the native method returns a value, the return value of the platform-dependent code is converted in an implementation-dependent way to the return type of the native method and pushed onto the operand stack.
During resolution of the symbolic reference to the method, any of the exceptions pertaining to method resolution (§5.4.3.3) can be thrown.
Otherwise, if the resolved method is an instance initialization method, and the class in which it is declared is not the class symbolically referenced by the instruction, a NoSuchMethodError is thrown.
Otherwise, if the resolved method is a class (static) method, the invokespecial instruction throws an IncompatibleClassChangeError.
Otherwise, if objectref is null, the invokespecial instruction throws a NullPointerException.
Otherwise, if step 1, step 2, or step 3 of the lookup procedure selects an abstract method, invokespecial throws an AbstractMethodError.
Otherwise, if step 1, step 2, or step 3 of the lookup procedure selects a native method and the code that implements the method cannot be bound, invokespecial throws an UnsatisfiedLinkError.
Otherwise, if step 4 of the lookup procedure determines there are multiple maximally-specific superinterface methods of C that match the resolved method's name and descriptor and are not abstract, invokespecial throws an IncompatibleClassChangeError
Otherwise, if step 4 of the lookup procedure determines there are no maximally-specific superinterface methods of C that match the resolved method's name and descriptor and are not abstract, invokespecial throws an AbstractMethodError.
The difference between the invokespecial instruction and the invokevirtual instruction (§invokevirtual) is that invokevirtual invokes a method based on the class of the object. The invokespecial instruction is used to directly invoke instance initialization methods (§2.9.1) as well as methods of the current class and its supertypes.
The invokespecial instruction was named invokenonvirtual prior to JDK release 1.0.2.
The nargs argument values and objectref are not one-to-one with the first nargs+1 local variables. Argument values of types long and double must be stored in two consecutive local variables, thus more than nargs local variables may be required to pass nargs argument values to the invoked method.
The invokespecial instruction handles invocation of a non-abstract interface method, referenced either via a direct superinterface or via a superclass. In these cases, the rules for selection are essentially the same as those for invokeinterface (except that the search starts from a different class).
The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class (§2.6), where the value of the index is (indexbyte1 << 8) | indexbyte2. The run-time constant pool entry at the index must be a symbolic reference to a method or an interface method (§5.1), which gives the name and descriptor (§4.3.3) of the method or interface method as well as a symbolic reference to the class or interface in which the method or interface method is to be found. The named method is resolved (§5.4.3.3, §5.4.3.4).
The resolved method must not be an instance initialization method, or the class or interface initialization method (§2.9.1, §2.9.2).
The resolved method must be static, and therefore cannot be abstract.
On successful resolution of the method, the class or interface that declared the resolved method is initialized if that class or interface has not already been initialized (§5.5).
The operand stack must contain nargs argument values, where the number, type, and order of the values must be consistent with the descriptor of the resolved method.
If the method is synchronized, the monitor associated with the resolved Class object is entered or reentered as if by execution of a monitorenter instruction (§monitorenter) in the current thread.
If the method is not native, the nargs argument values are popped from the operand stack. A new frame is created on the Java Virtual Machine stack for the method being invoked. The nargs argument values are consecutively made the values of local variables of the new frame, with arg1 in local variable 0 (or, if arg1 is of type long or double, in local variables 0 and 1) and so on. Any argument value that is of a floating-point type undergoes value set conversion (§2.8.3) prior to being stored in a local variable. The new frame is then made current, and the Java Virtual Machine pc is set to the opcode of the first instruction of the method to be invoked. Execution continues with the first instruction of the method.
If the method is native and the platform-dependent code that implements it has not yet been bound (§5.6) into the Java Virtual Machine, that is done. The nargs argument values are popped from the operand stack and are passed as parameters to the code that implements the method. Any argument value that is of a floating-point type undergoes value set conversion (§2.8.3) prior to being passed as a parameter. The parameters are passed and the code is invoked in an implementation-dependent manner. When the platform-dependent code returns, the following take place:
If the native method is synchronized, the monitor associated with the resolved Class object is updated and possibly exited as if by execution of a monitorexit instruction (§monitorexit) in the current thread.
If the native method returns a value, the return value of the platform-dependent code is converted in an implementation-dependent way to the return type of the native method and pushed onto the operand stack.
During resolution of the symbolic reference to the method, any of the exceptions pertaining to method resolution (§5.4.3.3) can be thrown.
Otherwise, if the resolved method is an instance method, the invokestatic instruction throws an IncompatibleClassChangeError.
Otherwise, if execution of this invokestatic instruction causes initialization of the referenced class or interface, invokestatic may throw an Error as detailed in §5.5.
Otherwise, if the resolved method is native and the code that implements the method cannot be bound, invokestatic throws an UnsatisfiedLinkError.
The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class (§2.6), where the value of the index is (indexbyte1 << 8) | indexbyte2. The run-time constant pool entry at the index must be a symbolic reference to a method (§5.1), which gives the name and descriptor (§4.3.3) of the method as well as a symbolic reference to the class in which the method is to be found. The named method is resolved (§5.4.3.3).
If the resolved method is not signature polymorphic (§2.9.3), then the invokevirtual instruction proceeds as follows.
Let C be the class of objectref. A method is selected with respect to C and the resolved method (§5.4.6). This is the method to be invoked.
The objectref must be followed on the operand stack by nargs argument values, where the number, type, and order of the values must be consistent with the descriptor of the selected instance method.
If the method to be invoked is synchronized, the monitor associated with objectref is entered or reentered as if by execution of a monitorenter instruction (§monitorenter) in the current thread.
If the method to be invoked is not native, the nargs argument values and objectref are popped from the operand stack. A new frame is created on the Java Virtual Machine stack for the method being invoked. The objectref and the argument values are consecutively made the values of local variables of the new frame, with objectref in local variable 0, arg1 in local variable 1 (or, if arg1 is of type long or double, in local variables 1 and 2), and so on. Any argument value that is of a floating-point type undergoes value set conversion (§2.8.3) prior to being stored in a local variable. The new frame is then made current, and the Java Virtual Machine pc is set to the opcode of the first instruction of the method to be invoked. Execution continues with the first instruction of the method.
If the method to be invoked is native and the platform-dependent code that implements it has not yet been bound (§5.6) into the Java Virtual Machine, that is done. The nargs argument values and objectref are popped from the operand stack and are passed as parameters to the code that implements the method. Any argument value that is of a floating-point type undergoes value set conversion (§2.8.3) prior to being passed as a parameter. The parameters are passed and the code is invoked in an implementation-dependent manner. When the platform-dependent code returns, the following take place:
If the native method is synchronized, the monitor associated with objectref is updated and possibly exited as if by execution of a monitorexit instruction (§monitorexit) in the current thread.
If the native method returns a value, the return value of the platform-dependent code is converted in an implementation-dependent way to the return type of the native method and pushed onto the operand stack.
If the resolved method is signature polymorphic (§2.9.3), and declared in the java.lang.invoke.MethodHandle class, then the invokevirtual instruction proceeds as follows, where D is the descriptor of the method symbolically referenced by the instruction.
First, a reference to an instance of java.lang.invoke.MethodType is obtained as if by resolution of a symbolic reference to a method type (§5.4.3.5) with the same parameter and return types as D.
If the named method is invokeExact, the instance of java.lang.invoke.MethodType must be semantically equal to the type descriptor of the receiving method handle objectref. The method handle to be invoked is objectref.
If the named method is invoke, and the instance of java.lang.invoke.MethodType is semantically equal to the type descriptor of the receiving method handle objectref, then the method handle to be invoked is objectref.
If the named method is invoke, and the instance of java.lang.invoke.MethodType is not semantically equal to the type descriptor of the receiving method handle objectref, then the Java Virtual Machine attempts to adjust the type descriptor of the receiving method handle, as if by invocation of the asType method of java.lang.invoke.MethodHandle, to obtain an exactly invokable method handle m. The method handle to be invoked is m.
The objectref must be followed on the operand stack by nargs argument values, where the number, type, and order of the values must be consistent with the type descriptor of the method handle to be invoked. (This type descriptor will correspond to the method descriptor appropriate for the kind of the method handle to be invoked, as specified in §5.4.3.5.)
Then, if the method handle to be invoked has bytecode behavior, the Java Virtual Machine invokes the method handle as if by execution of the bytecode behavior associated with the method handle's kind. If the kind is 5 (REF_invokeVirtual), 6 (REF_invokeStatic), 7 (REF_invokeSpecial), 8 (REF_newInvokeSpecial), or 9 (REF_invokeInterface), then a frame will be created and made current in the course of executing the bytecode behavior; however, this frame is not visible, and when the method invoked by the bytecode behavior completes (normally or abruptly), the frame of its invoker is considered to be the frame for the method containing this invokevirtual instruction.
Otherwise, if the method handle to be invoked has no bytecode behavior, the Java Virtual Machine invokes it in an implementation-dependent manner.
If the resolved method is signature polymorphic and declared in the java.lang.invoke.VarHandle class, then the invokevirtual instruction proceeds as follows, where N and D are the name and descriptor of the method symbolically referenced by the instruction.
First, a reference to an instance of java.lang.invoke.VarHandle.AccessMode is obtained as if by invocation of the valueFromMethodName method of java.lang.invoke.VarHandle.AccessMode with a String argument denoting N.
Second, a reference to an instance of java.lang.invoke.MethodType is obtained as if by invocation of the accessModeType method of java.lang.invoke.VarHandle on the instance objectref, with the instance of java.lang.invoke.VarHandle.AccessMode as the argument.
Third, a reference to an instance of java.lang.invoke.MethodHandle is obtained as if by invocation of the varHandleExactInvoker method of java.lang.invoke.MethodHandles with the instance of java.lang.invoke.VarHandle.AccessMode as the first argument and the instance of java.lang.invoke.MethodType as the second argument. The resulting instance is called the invoker method handle.
Finally, the nargs argument values and objectref are popped from the operand stack, and the invoker method handle is invoked. The invocation occurs as if by execution of an invokevirtual instruction that indicates a run-time constant pool index to a symbolic reference R where:
for the symbolic reference to the class in which the method is to be found, R specifies java.lang.invoke.MethodHandle;
for the descriptor of the method, R specifies a return type indicated by the return descriptor of D, and specifies a first parameter type of java.lang.invoke.VarHandle followed by the parameter types indicated by the parameter descriptors of D (if any) in order.
and where it is as if the following items were pushed, in order, onto the operand stack:
During resolution of the symbolic reference to the method, any of the exceptions pertaining to method resolution (§5.4.3.3) can be thrown.
Otherwise, if the resolved method is a class (static) method, the invokevirtual instruction throws an IncompatibleClassChangeError.
Otherwise, if the resolved method is signature polymorphic and declared in the java.lang.invoke.MethodHandle class, then during resolution of the method type derived from the descriptor in the symbolic reference to the method, any of the exceptions pertaining to method type resolution (§5.4.3.5) can be thrown.
Otherwise, if the resolved method is signature polymorphic and declared in the java.lang.invoke.VarHandle class, then any linking exception that may arise from invocation of the invoker method handle can be thrown. No linking exceptions are thrown from invocation of the valueFromMethodName, accessModeType, and varHandleExactInvoker methods.
Otherwise, if objectref is null, the invokevirtual instruction throws a NullPointerException.
Otherwise, if the resolved method is not signature polymorphic:
If the selected method is abstract, invokevirtual throws an AbstractMethodError.
Otherwise, if the selected method is native and the code that implements the method cannot be bound, invokevirtual throws an UnsatisfiedLinkError.
Otherwise, if no method is selected, and there are multiple maximally-specific superinterface methods of C that match the resolved method's name and descriptor and are not abstract, invokevirtual throws an IncompatibleClassChangeError
Otherwise, if no method is selected, and there are no maximally-specific superinterface methods of C that match the resolved method's name and descriptor and are not abstract, invokevirtual throws an AbstractMethodError.
Otherwise, if the resolved method is signature polymorphic and declared in the java.lang.invoke.MethodHandle class, then:
If the method name is invokeExact, and the obtained instance of java.lang.invoke.MethodType is not semantically equal to the type descriptor of the receiving method handle objectref, the invokevirtual instruction throws a java.lang.invoke.WrongMethodTypeException.
If the method name is invoke, and the obtained instance of java.lang.invoke.MethodType is not a valid argument to the asType method of java.lang.invoke.MethodHandle invoked on the receiving method handle objectref, the invokevirtual instruction throws a java.lang.invoke.WrongMethodTypeException.
Otherwise, if the resolved method is signature polymorphic and declared in the java.lang.invoke.VarHandle class, then any run-time exception that may arise from invocation of the invoker method handle can be thrown. No run-time exceptions are thrown from invocation of the valueFromMethodName, accessModeType, and varHandleExactInvoker methods, except NullPointerException if objectref is null.
The nargs argument values and objectref are not one-to-one with the first nargs+1 local variables. Argument values of types long and double must be stored in two consecutive local variables, thus more than nargs local variables may be required to pass nargs argument values to the invoked method.
It is possible that the symbolic reference of an invokevirtual instruction resolves to an interface method. In this case, it is possible that there is no overriding method in the class hierarchy, but that a non-abstract interface method matches the resolved method's descriptor. The selection logic matches such a method, using the same rules as for invokeinterface.
Both value1 and value2 must be of type int. The values are popped from the operand stack. The int result is value1 - (value1 / value2) * value2. The result is pushed onto the operand stack.
The result of the irem instruction is such that (a/b)*b + (a%b) is equal to a. This identity holds even in the special case in which the dividend is the negative int of largest possible magnitude for its type and the divisor is -1 (the remainder is 0). It follows from this rule that the result of the remainder operation can be negative only if the dividend is negative and can be positive only if the dividend is positive. Moreover, the magnitude of the result is always less than the magnitude of the divisor.
The current method must have return type boolean, byte, char, short, or int. The value must be of type int. If the current method is a synchronized method, the monitor entered or reentered on invocation of the method is updated and possibly exited as if by execution of a monitorexit instruction (§monitorexit) in the current thread. If no exception is thrown, value is popped from the operand stack of the current frame (§2.6) and pushed onto the operand stack of the frame of the invoker. Any other values on the operand stack of the current method are discarded.
Prior to pushing value onto the operand stack of the frame of the invoker, it may have to be converted. If the return type of the invoked method was byte, char, or short, then value is converted from int to the return type as if by execution of i2b, i2c, or i2s, respectively. If the return type of the invoked method was boolean, then value is narrowed from int to boolean by taking the bitwise AND of value and 1.
The interpreter then returns control to the invoker of the method, reinstating the frame of the invoker.
If the Java Virtual Machine implementation does not enforce the rules on structured locking described in §2.11.10, then if the current method is a synchronized method and the current thread is not the owner of the monitor entered or reentered on invocation of the method, ireturn throws an IllegalMonitorStateException. This can happen, for example, if a synchronized method contains a monitorexit instruction, but no monitorenter instruction, on the object on which the method is synchronized.
Otherwise, if the Java Virtual Machine implementation enforces the rules on structured locking described in §2.11.10 and if the first of those rules is violated during invocation of the current method, then ireturn throws an IllegalMonitorStateException.
Both value1 and value2 must be of type int. The values are popped from the operand stack. An int result is calculated by shifting value1 right by s bit positions, with sign extension, where s is the value of the low 5 bits of value2. The result is pushed onto the operand stack.
The resulting value is floor(value1 / 2s), where s is value2 & 0x1f. For non-negative value1, this is equivalent to truncating int division by 2 to the power s. The shift distance actually used is always in the range 0 to 31, inclusive, as if value2 were subjected to a bitwise logical AND with the mask value 0x1f.
The index is an unsigned byte that must be an index into the local variable array of the current frame (§2.6). The value on the top of the operand stack must be of type int. It is popped from the operand stack, and the value of the local variable at index is set to value.
The istore opcode can be used in conjunction with the wide instruction (§wide) to access a local variable using a two-byte unsigned index.
The <n> must be an index into the local variable array of the current frame (§2.6). The value on the top of the operand stack must be of type int. It is popped from the operand stack, and the value of the local variable at <n> is set to value.
Both value1 and value2 must be of type int. The values are popped from the operand stack. The int result is value1 - value2. The result is pushed onto the operand stack.
For int subtraction, a-b produces the same result as a+(-b). For int values, subtraction from zero is the same as negation.
The result is the 32 low-order bits of the true mathematical result in a sufficiently wide two's-complement format, represented as a value of type int. If overflow occurs, then the sign of the result may not be the same as the sign of the mathematical difference of the two values.
Despite the fact that overflow may occur, execution of an isub instruction never throws a run-time exception.
Both value1 and value2 must be of type int. The values are popped from the operand stack. An int result is calculated by shifting value1 right by s bit positions, with zero extension, where s is the value of the low 5 bits of value2. The result is pushed onto the operand stack.
If value1 is positive and s is value2 & 0x1f, the result is the same as that of value1 >> s; if value1 is negative, the result is equal to the value of the expression (value1 >> s) + (2 << ~s). The addition of the (2 << ~s) term cancels out the propagated sign bit. The shift distance actually used is always in the range 0 to 31, inclusive.
The address of the opcode of the instruction immediately following this jsr instruction is pushed onto the operand stack as a value of type returnAddress. The unsigned branchbyte1 and branchbyte2 are used to construct a signed 16-bit offset, where the offset is (branchbyte1 << 8) | branchbyte2. Execution proceeds at that offset from the address of this jsr instruction. The target address must be that of an opcode of an instruction within the method that contains this jsr instruction.
Note that jsr pushes the address onto the operand stack and ret (§ret) gets it out of a local variable. This asymmetry is intentional.
In Oracle's implementation of a compiler for the Java programming language prior to Java SE 6, the jsr instruction was used with the ret instruction in the implementation of the finally clause (§3.13, §4.10.2.5).
The address of the opcode of the instruction immediately following this jsr_w instruction is pushed onto the operand stack as a value of type returnAddress. The unsigned branchbyte1, branchbyte2, branchbyte3, and branchbyte4 are used to construct a signed 32-bit offset, where the offset is (branchbyte1 << 24) | (branchbyte2 << 16) | (branchbyte3 << 8) | branchbyte4. Execution proceeds at that offset from the address of this jsr_w instruction. The target address must be that of an opcode of an instruction within the method that contains this jsr_w instruction.
Note that jsr_w pushes the address onto the operand stack and ret (§ret) gets it out of a local variable. This asymmetry is intentional.
In Oracle's implementation of a compiler for the Java programming language prior to Java SE 6, the jsr_w instruction was used with the ret instruction in the implementation of the finally clause (§3.13, §4.10.2.5).
Although the jsr_w instruction takes a 4-byte branch offset, other factors limit the size of a method to 65535 bytes (§4.11). This limit may be raised in a future release of the Java Virtual Machine.
The value on the top of the operand stack must be of type long. It is popped from the operand stack and converted to a double result using the round to nearest rounding policy (§2.8). The result is pushed onto the operand stack.
The value on the top of the operand stack must be of type long. It is popped from the operand stack and converted to a float result using the round to nearest rounding policy (§2.8). The result is pushed onto the operand stack.
Both value1 and value2 must be of type long. The values are popped from the operand stack. The long result is value1 + value2. The result is pushed onto the operand stack.
The result is the 64 low-order bits of the true mathematical result in a sufficiently wide two's-complement format, represented as a value of type long. If overflow occurs, the sign of the result may not be the same as the sign of the mathematical sum of the two values.
Despite the fact that overflow may occur, execution of an ladd instruction never throws a run-time exception.
The arrayref must be of type reference and must refer to an array whose components are of type long. The index must be of type int, and value must be of type long. The arrayref, index, and value are popped from the operand stack. The long value is stored as the component of the array indexed by index.
Both value1 and value2 must be of type long. They are both popped from the operand stack, and a signed integer comparison is performed. If value1 is greater than value2, the int value 1 is pushed onto the operand stack. If value1 is equal to value2, the int value 0 is pushed onto the operand stack. If value1 is less than value2, the int value -1 is pushed onto the operand stack.
The index is an unsigned byte that must be a valid index into the run-time constant pool of the current class (§2.5.5). The run-time constant pool entry at index must be loadable (§5.1), and not any of the following:
If the run-time constant pool entry is a numeric constant of type int or float, then the value of that numeric constant is pushed onto the operand stack as an int or float, respectively.
Otherwise, if the run-time constant pool entry is a string constant, that is, a reference to an instance of class String, then value, a reference to that instance, is pushed onto the operand stack.
Otherwise, if the run-time constant pool entry is a symbolic reference to a class or interface, then the named class or interface is resolved (§5.4.3.1) and value, a reference to the Class object representing that class or interface, is pushed onto the operand stack.
Otherwise, the run-time constant pool entry is a symbolic reference to a method type, a method handle, or a dynamically-computed constant. The symbolic reference is resolved (§5.4.3.5, §5.4.3.6) and value, the result of resolution, is pushed onto the operand stack.
The unsigned indexbyte1 and indexbyte2 are assembled into an unsigned 16-bit index into the run-time constant pool of the current class (§2.5.5), where the value of the index is calculated as (indexbyte1 << 8) | indexbyte2. The index must be a valid index into the run-time constant pool of the current class. The run-time constant pool entry at the index must be loadable (§5.1), and not any of the following:
If the run-time constant pool entry is a numeric constant of type int or float, or a string constant, then value is determined and pushed onto the operand stack according to the rules given for the ldc instruction.
Otherwise, the run-time constant pool entry is a symbolic reference to a class, interface, method type, method handle, or dynamically-computed constant. It is resolved and value is determined and pushed onto the operand stack according to the rules given for the ldc instruction.
During resolution of a symbolic reference, any of the exceptions pertaining to resolution of that kind of symbolic reference can be thrown.
The ldc_w instruction is identical to the ldc instruction (§ldc) except for its wider run-time constant pool index.
The ldc_w instruction can only be used to push a value of type float taken from the float value set (§2.3.2) because a constant of type float in the constant pool (§4.4.4) must be taken from the float value set.
The unsigned indexbyte1 and indexbyte2 are assembled into an unsigned 16-bit index into the run-time constant pool of the current class (§2.5.5), where the value of the index is calculated as (indexbyte1 << 8) | indexbyte2. The index must be a valid index into the run-time constant pool of the current class. The run-time constant pool entry at the index must be loadable (§5.1), and in particular one of the following:
If the run-time constant pool entry is a numeric constant of type long or double, then the value of that numeric constant is pushed onto the operand stack as a long or double, respectively.
Otherwise, the run-time constant pool entry is a symbolic reference to a dynamically-computed constant. The symbolic reference is resolved (§5.4.3.6) and value, the result of resolution, is pushed onto the operand stack.
During resolution of a symbolic reference to a dynamically-computed constant, any of the exceptions pertaining to dynamically-computed constant resolution can be thrown.
Only a wide-index version of the ldc2_w instruction exists; there is no ldc2 instruction that pushes a long or double with a single-byte index.
The ldc2_w instruction can only be used to push a value of type double taken from the double value set (§2.3.2) because a constant of type double in the constant pool (§4.4.5) must be taken from the double value set.
Both value1 and value2 must be of type long. The values are popped from the operand stack. The long result is the value of the Java programming language expression value1 / value2. The result is pushed onto the operand stack.
A long division rounds towards 0; that is, the quotient produced for long values in n / d is a long value q whose magnitude is as large as possible while satisfying |d ⋅ q| ≤ |n|. Moreover, q is positive when |n| ≥ |d| and n and d have the same sign, but q is negative when |n| ≥ |d| and n and d have opposite signs.
There is one special case that does not satisfy this rule: if the dividend is the negative integer of largest possible magnitude for the long type and the divisor is -1, then overflow occurs and the result is equal to the dividend; despite the overflow, no exception is thrown in this case.
The index is an unsigned byte. Both index and index+1 must be indices into the local variable array of the current frame (§2.6). The local variable at index must contain a long. The value of the local variable at index is pushed onto the operand stack.
The lload opcode can be used in conjunction with the wide instruction (§wide) to access a local variable using a two-byte unsigned index.
Both <n> and <n>+1 must be indices into the local variable array of the current frame (§2.6). The local variable at <n> must contain a long. The value of the local variable at <n> is pushed onto the operand stack.
Both value1 and value2 must be of type long. The values are popped from the operand stack. The long result is value1 * value2. The result is pushed onto the operand stack.
The result is the 64 low-order bits of the true mathematical result in a sufficiently wide two's-complement format, represented as a value of type long. If overflow occurs, the sign of the result may not be the same as the sign of the mathematical multiplication of the two values.
Despite the fact that overflow may occur, execution of an lmul instruction never throws a run-time exception.
The value must be of type long. It is popped from the operand stack. The long result is the arithmetic negation of value, -value. The result is pushed onto the operand stack.
For long values, negation is the same as subtraction from zero. Because the Java Virtual Machine uses two's-complement representation for integers and the range of two's-complement values is not symmetric, the negation of the maximum negative long results in that same maximum negative number. Despite the fact that overflow has occurred, no exception is thrown.
lookupswitch
<0-3 byte pad>
defaultbyte1
defaultbyte2
defaultbyte3
defaultbyte4
npairs1
npairs2
npairs3
npairs4
match-offset pairs...
A lookupswitch is a variable-length instruction. Immediately after the lookupswitch opcode, between zero and three bytes must act as padding, such that defaultbyte1 begins at an address that is a multiple of four bytes from the start of the current method (the opcode of its first instruction). Immediately after the padding follow a series of signed 32-bit values: default, npairs, and then npairs pairs of signed 32-bit values. The npairs must be greater than or equal to 0. Each of the npairs pairs consists of an int match and a signed 32-bit offset. Each of these signed 32-bit values is constructed from four unsigned bytes as (byte1 << 24) | (byte2 << 16) | (byte3 << 8) | byte4.
The table match-offset pairs of the lookupswitch instruction must be sorted in increasing numerical order by match.
The key must be of type int and is popped from the operand stack. The key is compared against the match values. If it is equal to one of them, then a target address is calculated by adding the corresponding offset to the address of the opcode of this lookupswitch instruction. If the key does not match any of the match values, the target address is calculated by adding default to the address of the opcode of this lookupswitch instruction. Execution then continues at the target address.
The target address that can be calculated from the offset of each match-offset pair, as well as the one calculated from default, must be the address of an opcode of an instruction within the method that contains this lookupswitch instruction.
The alignment required of the 4-byte operands of the lookupswitch instruction guarantees 4-byte alignment of those operands if and only if the method that contains the lookupswitch is positioned on a 4-byte boundary.
The match-offset pairs are sorted to support lookup routines that are quicker than linear search.
Both value1 and value2 must be of type long. The values are popped from the operand stack. The long result is value1 - (value1 / value2) * value2. The result is pushed onto the operand stack.
The result of the lrem instruction is such that (a/b)*b + (a%b) is equal to a. This identity holds even in the special case in which the dividend is the negative long of largest possible magnitude for its type and the divisor is -1 (the remainder is 0). It follows from this rule that the result of the remainder operation can be negative only if the dividend is negative and can be positive only if the dividend is positive; moreover, the magnitude of the result is always less than the magnitude of the divisor.
The current method must have return type long. The value must be of type long. If the current method is a synchronized method, the monitor entered or reentered on invocation of the method is updated and possibly exited as if by execution of a monitorexit instruction (§monitorexit) in the current thread. If no exception is thrown, value is popped from the operand stack of the current frame (§2.6) and pushed onto the operand stack of the frame of the invoker. Any other values on the operand stack of the current method are discarded.
The interpreter then returns control to the invoker of the method, reinstating the frame of the invoker.
If the Java Virtual Machine implementation does not enforce the rules on structured locking described in §2.11.10, then if the current method is a synchronized method and the current thread is not the owner of the monitor entered or reentered on invocation of the method, lreturn throws an IllegalMonitorStateException. This can happen, for example, if a synchronized method contains a monitorexit instruction, but no monitorenter instruction, on the object on which the method is synchronized.
Otherwise, if the Java Virtual Machine implementation enforces the rules on structured locking described in §2.11.10 and if the first of those rules is violated during invocation of the current method, then lreturn throws an IllegalMonitorStateException.
The value1 must be of type long, and value2 must be of type int. The values are popped from the operand stack. A long result is calculated by shifting value1 right by s bit positions, with sign extension, where s is the value of the low 6 bits of value2. The result is pushed onto the operand stack.
The resulting value is floor(value1 / 2s), where s is value2 & 0x3f. For non-negative value1, this is equivalent to truncating long division by 2 to the power s. The shift distance actually used is therefore always in the range 0 to 63, inclusive, as if value2 were subjected to a bitwise logical AND with the mask value 0x3f.
The index is an unsigned byte. Both index and index+1 must be indices into the local variable array of the current frame (§2.6). The value on the top of the operand stack must be of type long. It is popped from the operand stack, and the local variables at index and index+1 are set to value.
The lstore opcode can be used in conjunction with the wide instruction (§wide) to access a local variable using a two-byte unsigned index.
Both <n> and <n>+1 must be indices into the local variable array of the current frame (§2.6). The value on the top of the operand stack must be of type long. It is popped from the operand stack, and the local variables at <n> and <n>+1 are set to value.
Both value1 and value2 must be of type long. The values are popped from the operand stack. The long result is value1 - value2. The result is pushed onto the operand stack.
For long subtraction, a-b produces the same result as a+(-b). For long values, subtraction from zero is the same as negation.
The result is the 64 low-order bits of the true mathematical result in a sufficiently wide two's-complement format, represented as a value of type long. If overflow occurs, then the sign of the result may not be the same as the sign of the mathematical difference of the two values.
Despite the fact that overflow may occur, execution of an lsub instruction never throws a run-time exception.
The value1 must be of type long, and value2 must be of type int. The values are popped from the operand stack. A long result is calculated by shifting value1 right logically by s bit positions, with zero extension, where s is the value of the low 6 bits of value2. The result is pushed onto the operand stack.
If value1 is positive and s is value2 & 0x3f, the result is the same as that of value1 >> s; if value1 is negative, the result is equal to the value of the expression (value1 >> s) + (2L << ~s). The addition of the (2L << ~s) term cancels out the propagated sign bit. The shift distance actually used is always in the range 0 to 63, inclusive.
The objectref must be of type reference.
Each object is associated with a monitor. A monitor is locked if and only if it has an owner. The thread that executes monitorenter attempts to gain ownership of the monitor associated with objectref, as follows:
If the entry count of the monitor associated with objectref is zero, the thread enters the monitor and sets its entry count to one. The thread is then the owner of the monitor.
If the thread already owns the monitor associated with objectref, it reenters the monitor, incrementing its entry count.
If another thread already owns the monitor associated with objectref, the thread blocks until the monitor's entry count is zero, then tries again to gain ownership.
A monitorenter instruction may be used with one or more monitorexit instructions (§monitorexit) to implement a synchronized statement in the Java programming language (§3.14). The monitorenter and monitorexit instructions are not used in the implementation of synchronized methods, although they can be used to provide equivalent locking semantics. Monitor entry on invocation of a synchronized method, and monitor exit on its return, are handled implicitly by the Java Virtual Machine's method invocation and return instructions, as if monitorenter and monitorexit were used.
The association of a monitor with an object may be managed in various ways that are beyond the scope of this specification. For instance, the monitor may be allocated and deallocated at the same time as the object. Alternatively, it may be dynamically allocated at the time when a thread attempts to gain exclusive access to the object and freed at some later time when no thread remains in the monitor for the object.
The synchronization constructs of the Java programming language require support for operations on monitors besides entry and exit. These include waiting on a monitor (Object.wait) and notifying other threads waiting on a monitor (Object.notifyAll and Object.notify). These operations are supported in the standard package java.lang supplied with the Java Virtual Machine. No explicit support for these operations appears in the instruction set of the Java Virtual Machine.
The objectref must be of type reference.
The thread that executes monitorexit must be the owner of the monitor associated with the instance referenced by objectref.
The thread decrements the entry count of the monitor associated with objectref. If as a result the value of the entry count is zero, the thread exits the monitor and is no longer its owner. Other threads that are blocking to enter the monitor are allowed to attempt to do so.
If objectref is null, monitorexit throws a NullPointerException.
Otherwise, if the thread that executes monitorexit is not the owner of the monitor associated with the instance referenced by objectref, monitorexit throws an IllegalMonitorStateException.
Otherwise, if the Java Virtual Machine implementation enforces the rules on structured locking described in §2.11.10 and if the second of those rules is violated by the execution of this monitorexit instruction, then monitorexit throws an IllegalMonitorStateException.
One or more monitorexit instructions may be used with a monitorenter instruction (§monitorenter) to implement a synchronized statement in the Java programming language (§3.14). The monitorenter and monitorexit instructions are not used in the implementation of synchronized methods, although they can be used to provide equivalent locking semantics.
The Java Virtual Machine supports exceptions thrown within synchronized methods and synchronized statements differently:
Monitor exit on normal synchronized method completion is handled by the Java Virtual Machine's return instructions. Monitor exit on abrupt synchronized method completion is handled implicitly by the Java Virtual Machine's athrow instruction.
When an exception is thrown from within a synchronized statement, exit from the monitor entered prior to the execution of the synchronized statement is achieved using the Java Virtual Machine's exception handling mechanism (§3.14).
The dimensions operand is an unsigned byte that must be greater than or equal to 1. It represents the number of dimensions of the array to be created. The operand stack must contain dimensions values. Each such value represents the number of components in a dimension of the array to be created, must be of type int, and must be non-negative. The count1 is the desired length in the first dimension, count2 in the second, etc.
All of the count values are popped off the operand stack. The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class (§2.6), where the value of the index is (indexbyte1 << 8) | indexbyte2. The run-time constant pool entry at the index must be a symbolic reference to a class, array, or interface type. The named class, array, or interface type is resolved (§5.4.3.1). The resulting entry must be an array class type of dimensionality greater than or equal to dimensions.
A new multidimensional array of the array type is allocated from the garbage-collected heap. If any count value is zero, no subsequent dimensions are allocated. The components of the array in the first dimension are initialized to subarrays of the type of the second dimension, and so on. The components of the last allocated dimension of the array are initialized to the default initial value (§2.3, §2.4) for the element type of the array type. A reference arrayref to the new array is pushed onto the operand stack.
During resolution of the symbolic reference to the class, array, or interface type, any of the exceptions documented in §5.4.3.1 can be thrown.
Otherwise, if the current class does not have permission to access the element type of the resolved array class, multianewarray throws an IllegalAccessError.
Otherwise, if any of the dimensions values on the operand stack are less than zero, the multianewarray instruction throws a NegativeArraySizeException.
It may be more efficient to use newarray or anewarray (§newarray, §anewarray) when creating an array of a single dimension.
The array class referenced via the run-time constant pool may have more dimensions than the dimensions operand of the multianewarray instruction. In that case, only the first dimensions of the dimensions of the array are created.
The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class (§2.6), where the value of the index is (indexbyte1 << 8) | indexbyte2. The run-time constant pool entry at the index must be a symbolic reference to a class or interface type. The named class or interface type is resolved (§5.4.3.1) and should result in a class type. Memory for a new instance of that class is allocated from the garbage-collected heap, and the instance variables of the new object are initialized to their default initial values (§2.3, §2.4). The objectref, a reference to the instance, is pushed onto the operand stack.
On successful resolution of the class, it is initialized if it has not already been initialized (§5.5).
During resolution of the symbolic reference to the class or interface type, any of the exceptions documented in §5.4.3.1 can be thrown.
Otherwise, if the symbolic reference to the class or interface type resolves to an interface or an abstract class, new throws an InstantiationError.
Otherwise, if execution of this new instruction causes initialization of the referenced class, new may throw an Error as detailed in JLS §15.9.4.
The new instruction does not completely create a new instance; instance creation is not completed until an instance initialization method (§2.9.1) has been invoked on the uninitialized instance.
The count must be of type int. It is popped off the operand stack. The count represents the number of elements in the array to be created.
The atype is a code that indicates the type of array to create. It must take one of the following values:
Table 6.5.newarray-A. Array type codes
| Array Type | atype |
|---|---|
T_BOOLEAN | 4 |
T_CHAR | 5 |
T_FLOAT | 6 |
T_DOUBLE | 7 |
T_BYTE | 8 |
T_SHORT | 9 |
T_INT | 10 |
T_LONG | 11 |
A new array whose components are of type atype and of length count is allocated from the garbage-collected heap. A reference arrayref to this new array object is pushed into the operand stack. Each of the elements of the new array is initialized to the default initial value (§2.3, §2.4) for the element type of the array type.
In Oracle's Java Virtual Machine implementation, arrays of type boolean (atype is T_BOOLEAN) are stored as arrays of 8-bit values and are manipulated using the baload and bastore instructions (§baload, §bastore) which also access arrays of type byte. Other implementations may implement packed boolean arrays; the baload and bastore instructions must still be used to access those arrays.
Pop the top value from the operand stack.
The pop instruction must not be used unless value is a value of a category 1 computational type (§2.11.1).
The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class (§2.6), where the value of the index is (indexbyte1 << 8) | indexbyte2. The run-time constant pool entry at the index must be a symbolic reference to a field (§5.1), which gives the name and descriptor of the field as well as a symbolic reference to the class in which the field is to be found. The referenced field is resolved (§5.4.3.2).
The type of a value stored by a putfield instruction must be compatible with the descriptor of the referenced field (§4.3.2). If the field descriptor type is boolean, byte, char, short, or int, then the value must be an int. If the field descriptor type is float, long, or double, then the value must be a float, long, or double, respectively. If the field descriptor type is a reference type, then the value must be of a type that is assignment compatible (JLS §5.2) with the field descriptor type. If the field is final, it must be declared in the current class, and the instruction must occur in an instance initialization method of the current class (§2.9.1).
The value and objectref are popped from the operand stack.
The objectref must be of type reference but not an array type.
If the value is of type int and the field descriptor type is boolean, then the int value is narrowed by taking the bitwise AND of value and 1, resulting in value'. Otherwise, the value undergoes value set conversion (§2.8.3), resulting in value'.
During resolution of the symbolic reference to the field, any of the exceptions pertaining to field resolution (§5.4.3.2) can be thrown.
Otherwise, if the resolved field is a static field, putfield throws an IncompatibleClassChangeError.
Otherwise, if the resolved field is final, it must be declared in the current class, and the instruction must occur in an instance initialization method of the current class. Otherwise, an IllegalAccessError is thrown.
The unsigned indexbyte1 and indexbyte2 are used to construct an index into the run-time constant pool of the current class (§2.6), where the value of the index is (indexbyte1 << 8) | indexbyte2. The run-time constant pool entry at the index must be a symbolic reference to a field (§5.1), which gives the name and descriptor of the field as well as a symbolic reference to the class or interface in which the field is to be found. The referenced field is resolved (§5.4.3.2).
On successful resolution of the field, the class or interface that declared the resolved field is initialized if that class or interface has not already been initialized (§5.5).
The type of a value stored by a putstatic instruction must be compatible with the descriptor of the referenced field (§4.3.2). If the field descriptor type is boolean, byte, char, short, or int, then the value must be an int. If the field descriptor type is float, long, or double, then the value must be a float, long, or double, respectively. If the field descriptor type is a reference type, then the value must be of a type that is assignment compatible (JLS §5.2) with the field descriptor type. If the field is final, it must be declared in the current class or interface, and the instruction must occur in the class or interface initialization method of the current class or interface (§2.9.2).
The value is popped from the operand stack.
If the value is of type int and the field descriptor type is boolean, then the int value is narrowed by taking the bitwise AND of value and 1, resulting in value'. Otherwise, the value undergoes value set conversion (§2.8.3), resulting in value'.
The referenced field in the class or interface is set to value'.
During resolution of the symbolic reference to the class or interface field, any of the exceptions pertaining to field resolution (§5.4.3.2) can be thrown.
Otherwise, if the resolved field is not a static (class) field or an interface field, putstatic throws an IncompatibleClassChangeError.
Otherwise, if the resolved field is final, it must be declared in the current class or interface, and the instruction must occur in the class or interface initialization method of the current class or interface. Otherwise, an IllegalAccessError is thrown.
Otherwise, if execution of this putstatic instruction causes initialization of the referenced class or interface, putstatic may throw an Error as detailed in §5.5.
A putstatic instruction may be used only to set the value of an interface field on the initialization of that field. Interface fields may be assigned to only once, on execution of an interface variable initialization expression when the interface is initialized (§5.5, JLS §9.3.1).
The index is an unsigned byte between 0 and 255, inclusive. The local variable at index in the current frame (§2.6) must contain a value of type returnAddress. The contents of the local variable are written into the Java Virtual Machine's pc register, and execution continues there.
Note that jsr (§jsr) pushes the address onto the operand stack and ret gets it out of a local variable. This asymmetry is intentional.
In Oracle's implementation of a compiler for the Java programming language prior to Java SE 6, the ret instruction was used with the jsr and jsr_w instructions (§jsr, §jsr_w) in the implementation of the finally clause (§3.13, §4.10.2.5).
The ret instruction should not be confused with the return instruction (§return). A return instruction returns control from a method to its invoker, without passing any value back to the invoker.
The ret opcode can be used in conjunction with the wide instruction (§wide) to access a local variable using a two-byte unsigned index.
The current method must have return type void. If the current method is a synchronized method, the monitor entered or reentered on invocation of the method is updated and possibly exited as if by execution of a monitorexit instruction (§monitorexit) in the current thread. If no exception is thrown, any values on the operand stack of the current frame (§2.6) are discarded.
The interpreter then returns control to the invoker of the method, reinstating the frame of the invoker.
If the Java Virtual Machine implementation does not enforce the rules on structured locking described in §2.11.10, then if the current method is a synchronized method and the current thread is not the owner of the monitor entered or reentered on invocation of the method, return throws an IllegalMonitorStateException. This can happen, for example, if a synchronized method contains a monitorexit instruction, but no monitorenter instruction, on the object on which the method is synchronized.
Otherwise, if the Java Virtual Machine implementation enforces the rules on structured locking described in §2.11.10 and if the first of those rules is violated during invocation of the current method, then return throws an IllegalMonitorStateException.
The arrayref must be of type reference and must refer to an array whose components are of type short. The index must be of type int. Both arrayref and index are popped from the operand stack. The component of the array at index is retrieved and sign-extended to an int value. That value is pushed onto the operand stack.
The arrayref must be of type reference and must refer to an array whose components are of type short. Both index and value must be of type int. The arrayref, index, and value are popped from the operand stack. The int value is truncated to a short and stored as the component of the array indexed by index.
Swap the top two values on the operand stack.
The swap instruction must not be used unless value1 and value2 are both values of a category 1 computational type (§2.11.1).
tableswitch
<0-3 byte pad>
defaultbyte1
defaultbyte2
defaultbyte3
defaultbyte4
lowbyte1
lowbyte2
lowbyte3
lowbyte4
highbyte1
highbyte2
highbyte3
highbyte4
jump offsets...
A tableswitch is a variable-length instruction. Immediately after the tableswitch opcode, between zero and three bytes must act as padding, such that defaultbyte1 begins at an address that is a multiple of four bytes from the start of the current method (the opcode of its first instruction). Immediately after the padding are bytes constituting three signed 32-bit values: default, low, and high. Immediately following are bytes constituting a series of high - low + 1 signed 32-bit offsets. The value low must be less than or equal to high. The high - low + 1 signed 32-bit offsets are treated as a 0-based jump table. Each of these signed 32-bit values is constructed as (byte1 << 24) | (byte2 << 16) | (byte3 << 8) | byte4.
The index must be of type int and is popped from the operand stack. If index is less than low or index is greater than high, then a target address is calculated by adding default to the address of the opcode of this tableswitch instruction. Otherwise, the offset at position index - low of the jump table is extracted. The target address is calculated by adding that offset to the address of the opcode of this tableswitch instruction. Execution then continues at the target address.
The target address that can be calculated from each jump table offset, as well as the one that can be calculated from default, must be the address of an opcode of an instruction within the method that contains this tableswitch instruction.
wide
<opcode>
indexbyte1
indexbyte2
where <opcode> is one of iload, fload, aload, lload, dload, istore, fstore, astore, lstore, dstore, or ret
The wide instruction modifies the behavior of another instruction. It takes one of two formats, depending on the instruction being modified. The first form of the wide instruction modifies one of the instructions iload, fload, aload, lload, dload, istore, fstore, astore, lstore, dstore, or ret (§iload, §fload, §aload, §lload, §dload, §istore, §fstore, §astore, §lstore, §dstore, §ret). The second form applies only to the iinc instruction (§iinc).
In either case, the wide opcode itself is followed in the compiled code by the opcode of the instruction wide modifies. In either form, two unsigned bytes indexbyte1 and indexbyte2 follow the modified opcode and are assembled into a 16-bit unsigned index to a local variable in the current frame (§2.6), where the value of the index is (indexbyte1 << 8) | indexbyte2. The calculated index must be an index into the local variable array of the current frame. Where the wide instruction modifies an lload, dload, lstore, or dstore instruction, the index following the calculated index (index + 1) must also be an index into the local variable array. In the second form, two immediate unsigned bytes constbyte1 and constbyte2 follow indexbyte1 and indexbyte2 in the code stream. Those bytes are also assembled into a signed 16-bit constant, where the constant is (constbyte1 << 8) | constbyte2.
The widened bytecode operates as normal, except for the use of the wider index and, in the case of the second form, the larger increment range.
Although we say that wide "modifies the behavior of another instruction," the wide instruction effectively treats the bytes constituting the modified instruction as operands, denaturing the embedded instruction in the process. In the case of a modified iinc instruction, one of the logical operands of the iinc is not even at the normal offset from the opcode. The embedded instruction must never be executed directly; its opcode must never be the target of any control transfer instruction.