finally
When exceptions are thrown, execution in a method takes a rather abrupt, nonlinear path
that alters the normal flow through the method. Depending upon how the method is coded,
it is even possible for an exception to cause the method to return prematurely. This could
be a problem in some methods. For example, if a method opens a file upon entry and
closes it upon exit, then you will not want the code that closes the file to be bypassed
by the exception-handling mechanism. The finally keyword is designed to address this
contingency.
finally creates a block of code that will be executed after a try/catch block has
completed and before the code following the try/catch block. The finally block will
execute whether or not an exception is thrown. If an exception is thrown, the finally
block will execute even if no catch statement matches the exception. Any time a method
is about to return to the caller from inside a try/catch block, via an uncaught exception or
an explicit return statement, the finally clause is also executed just before the method
returns. This can be useful for closing file handles and freeing up any other resources that
might have been allocated at the beginning of a method with the intent of disposing of them
before returning. The finally clause is optional. However, each try statement requires at
least one catch or a finally clause.
Here is an example program that shows three methods that exit in various ways, none
without executing their finally clauses:
// Demonstrate finally.
class FinallyDemo {
// Through an exception out of the method.
static void procA() {
try {
System.out.println("inside procA");
throw new RuntimeException("demo");
} finally {
System.out.println("procA's finally");
}
}
// Return from within a try block.
static void procB() {
try {
System.out.println("inside procB");
return;
} finally {
System.out.println("procB's finally");
}
}
// Execute a try block normally.
static void procC() {
try {
System.out.println("inside procC");
} finally {
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