Exception Handling - Java: A Beginner's Guide - page 426

In this example, an exception that can be handled by the inner try —in this case, a divide-
by-zero error—allows the program to continue. However, an array boundary error is caught
by the outer try , which causes the program to terminate.
Although certainly not the only reason for nested try statements, the preceding program
makes an important point that can be generalized. Often nested try blocks are used to allow
different categories of errors to be handled in different ways. Some types of errors are cata-
strophic and cannot be fixed. Some are minor and can be handled immediately. You might
use an outer try block to catch the most severe errors, allowing inner try blocks to handle
less serious ones.
Throwing an Exception
The preceding examples have been catching exceptions generated automatically by the
JVM. However, it is possible to manually throw an exception by using the throw statement.
Its general form is shown here:
throw exceptOb ;
Here, exceptOb must be an object of an exception class derived from Throwable .
Here is an example that illustrates the throw statement by manually throwing an Arith-
meticException :
The output from the program is shown here: