Java Reference
In-Depth Information
EXAMPLE
In the following, e is the catch block parameter.
catch (Exception e)
{
System.out.println(e.getMessage());
System.out.println("Aborting program.");
System.exit(0);
}
Let's consider two possible cases of what can happen when a try block is executed:
(1) no exception is thrown in the try block, and (2) an exception is thrown in the try
block and caught in the catch block. (Later we will describe a third case where the
catch block does not catch the exception.)
1. If no exception is thrown, the code in the try block is executed to the end of the try
block, the catch block is skipped, and execution continues with the code placed after
the catch block.
2. If an exception is thrown in the try block, the rest of the code in the try block is
skipped and (in simple cases) control is transferred to a following catch block. The
thrown object is plugged in for the catch block parameter, and the code in the
catch block is executed. And then (provided the catch block code does not end the
program or do something else to end the catch block code prematurely), the code
that follows that catch block is executed.
The getMessage Method
Every exception has a String instance variable that contains some message, which typically
identifies the reason for the exception. For example, if the exception is thrown as follows:
throw new Exception( String_Argument );
then the string given as an argument to the constructor Exception is used as the value of this
String instance variable. If the object is called e , then the method call e.getMessage()
returns this string.
EXAMPLE
Suppose the following throw statement is executed in a try block:
throw new Exception("Input must be positive.");
(continued)
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