This is not the right way to use assertions. In fact, Oracle has made clear that assertions should not check method parameters, and more importantly, one should never assert the result of a function call with a side effect (since there are no guarantees it will actually be executed).
They are designed to be used to check invariants (for example, a list class might include some elements and an int length, and that length must be equal to the number of elements). Another example of the correct use:
public Foo acquireFoo(int id) { Foo result = null; if (id > 50) { result = fooService.read(id); } else { result = new Foo(id); } assert result != null; return result; }
If the Java application is running with -ea on the command-line, then assertions will be enabled. When the application reaches assert (initialBalance > 0);, if initialBalance is less than 0 and assertions are enabled, a java.lang.AssertionError will be thrown. If -ea is not passed, then the assertion error will not be thrown.
It would be wiser to throw a java.lang.IllegalArgumentException as follows:
public BankAccount(int initialBalance) { if (initialBalance < 0){ throw new IllegalArgumentException("The initial balance may not be negative."); } balance = initialBalance; }
