Exceptions - Beginning Java - page 349

Try block entered i = 1 j = 0
Arithmetic exception caught
After try block
How It Works
The variable j is initialized to 0, so that the divide operation in the try block causes an ArithmeticEx-
ception exception to be thrown by the Java Virtual Machine. The first line in the try block enables you
to track when the try block is entered, and the second line throws an exception. The third line can be
executed only if the exception isn't thrown — which can't occur in this example.
The output shows that when the exception is thrown, control transfers immediately to the first statement
in the catch block. It's the evaluation of the expression that is the argument to the println() method
that throws the exception, so the println() method never gets called. After the catch block has been
executed, execution then continues with the statement following the catch block. The statements in the
try block following the point where the exception occurred aren't executed. You could try running the
example again after changing the value of j to 1 so that no exception is thrown. The output in this case
is:
Try block entered i = 1 j = 1
1
Ending try block
After try block
From this you can see that the entire try block is executed. Execution then continues with the statement
after the catch block. Because no arithmetic exception was thrown, the code in the catch block isn't
executed.
WARNING You need to take care when adding try blocks to existing code. A try
block is no different to any other block between braces when it comes to variable
scope. Variables declared in a try block are available only until the closing brace
for the block. It's easy to enclose the declaration of a variable in a try block, and,
in doing so, inadvertently limit the scope of the variable and cause compiler errors.
The catch block itself is a separate scope from the try block. If you want the catch block to output
information about objects or values that are set in the try block, make sure the variables are declared in
an outer scope.
try catch Bonding
The try and catch blocks are bonded together. You must not separate them by putting statements between
the two blocks, or even by putting braces around the try keyword and the try block itself. If you have a
loop block that is also a try block, the catch block that follows is also part of the loop. You can see this
with a variation of the previous example.