Exception Handling - Java - page 513

• An exception is caught in a catch block.

• A try block must be followed by at least one catch block and can be followed by

more than one catch block. If there are multiple catch blocks, always list the
catch block for a more specific exception class before the catch block for a more
general exception class.

• The best use of exceptions is to throw an exception in a method (but not catch it

in the method), but to only do this when the way the exception is handled will
vary from one invocation of the method to another. There is seldom any other sit-
uation that can profitably benefit from throwing an exception.

• If an exception is thrown in a method but not caught in that method, then if the

exception is not a descendent of the class RuntimeException (and is not a descen-
dent of the class Error ), the exception type must be listed in the throws clause for
that method.

Answers to Self-Test Exercises

1. Try block entered.
Over 30.
After catch block

2. The output would then be

Try block entered.
Under 30.
After catch block

3. There are two throw statements:

throw new Exception("Over 30.");
throw new Exception("Under 30.");

4. When a throw statement is executed, that is the end of the enclosing try block.
No other statements in the try block are executed, and control passes to the fol-
lowing catch block(s). When we say that control passes to the following catch
block, we mean that the exception object that is thrown is plugged in for the
catch block parameter and the code in the catch block is executed.
5. try
{
System.out.println("Try block entered.");
if (waitTime > 30)
throw new Exception("Over 30.");
else if (waitTime < 30)
throw new Exception("Under 30.");
else
System.out.println("No exception.");
System.out.println("Leaving try block.");
}