Exception Handling - Part 1

Exception Handling - Part 1

• 1.
  Core Java Training ExceptionHandling
• 2.
  Page 1Classification: Restricted Agenda •Exception Handling • Exception Class hierarchy • Types of Exception • Keywords for Exception Handling
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  Page 2Classification: Restricted Exceptions… •One of the powerful mechanism to handle the runtime errors so that normal flow of the application can be maintained. • In Java, exception is an event that disrupts the normal flow of the program. It is an object which is thrown at runtime. • Exception Handling is a mechanism to handle runtime errors such as ClassNotFound, IO, SQL, Remote etc.
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  Page 3Classification: Restricted ExceptionClass Hierarchy
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  Page 4Classification: Restricted Typesof Exception
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  Page 5Classification: Restricted Typesof Exception 1) Checked Exception The classes that extend Throwable class except RuntimeException and Error are known as checked exceptions e.g.IOException, SQLException etc. Checked exceptions are checked at compile-time. The programmer is compelled to handle (caught or declared) these in his code. 2) Unchecked Exception The classes that extend RuntimeException are known as unchecked exceptions e.g. ArithmeticException, NullPointerException, ArrayIndexOutOfBoundsException etc. Unchecked exceptions are not checked at compile-time rather they are checked at runtime. These are exceptions that the programmer is not compelled to handle in his code. 3) Error Error is irrecoverable e.g. OutOfMemoryError, VirtualMachineError, AssertionError etc.
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  Page 6Classification: Restricted Examples •ArithmeticException int a=50/0;//ArithmeticException • NullPointerException String s=null; System.out.println(s.length());//NullPointerException • NumberFormatException String s="abc"; int i=Integer.parseInt(s);//NumberFormatException • ArrayIndexOutOfBoundsException int a[]=new int[5]; a[10]=50; //ArrayIndexOutOfBoundsException
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  Page 7Classification: Restricted Keywordsfor Exception Handling • try • catch • finally • throw • throws
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  Page 8Classification: Restricted Problemwithout exception handling public class Testtrycatch1{ public static void main(String args[]){ int data=50/0;//may throw exception System.out.println("rest of the code..."); } }
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  Page 9Classification: Restricted Internalworking…
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  Page 10Classification: Restricted Solutionby exception handling public class Testtrycatch2{ public static void main(String args[]){ try{ int data=50/0; }catch(ArithmeticException e){System.out.println(e);} System.out.println("rest of the code..."); } }
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  Page 11Classification: Restricted Example… publicclass TestMultipleCatchBlock{ public static void main(String args[]){ try{ int a[]=new int[5]; a[5]=30/0; } catch(ArithmeticException e){System.out.println("task1 is completed");} catch(ArrayIndexOutOfBoundsException e){System.out.println("task 2 completed");} catch(Exception e){System.out.println("common task completed");} System.out.println("rest of the code..."); } } Rule: At a time only one Exception occurs and at a time only one catch block is executed. Rule: All catch blocks must be ordered from most specific to most general i.e. catch for ArithmeticException must come before catch for Exception.
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  Page 12Classification: Restricted Nestedtry catch blocks… class Excep6{ public static void main(String args[]){ try{ try{ System.out.println("going to divide"); int b =39/0; }catch(ArithmeticException e){System.out.println(e);} try{ int a[]=new int[5]; a[5]=4; }catch(ArrayIndexOutOfBoundsException e){System.out.println(e);} System.out.println("other statement); }catch(Exception e){System.out.println("handeled");} System.out.println("normal flow.."); } }
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  Page 13Classification: Restricted finallyblock • Java finally block is a block that is used to execute important code (releasing resources) such as closing connection, stream etc. • Java finally block is always executed whether exception is handled or not. • Java finally block follows try or catch block.
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  Page 14Classification: Restricted Examples… classTestFinallyBlock{ public static void main(String args[]){ try{ int data=25/5; System.out.println(data); } catch(NullPointerException e){System.out.println(e);} finally{System.out.println("finally block is always executed");} System.out.println("rest of the code..."); } }
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  Page 15Classification: Restricted Example:Exception occurs, not handled…but finally is executed. class TestFinallyBlock1{ public static void main(String args[]){ try{ int data=25/0; System.out.println(data); } catch(NullPointerException e){System.out.println(e);} finally{System.out.println("finally block is always executed");} System.out.println("rest of the code..."); } }
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  Page 16Classification: Restricted Example:Exception occurs and handled public class TestFinallyBlock2{ public static void main(String args[]){ try{ int data=25/0; System.out.println(data); } catch(ArithmeticException e){System.out.println(e);} finally{System.out.println("finally block is always executed");} System.out.println("rest of the code..."); } }
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  Page 17Classification: Restricted Morerules… • Rule: For each try block there can be zero or more catch blocks, but only one finally block. • Note: The finally block will not be executed if program exits(either by calling System.exit() or by causing a fatal error that causes the process to abort)
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  Page 18Classification: Restricted Topicsto be covered in next session • throw and throws keywords • Exception propagation – the cases of Checked and Unchecked Exceptions • Defining your own custom Exception
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  Page 19Classification: Restricted Thankyou!