Handling Errors Using Exceptions

Dealing with Exceptions

Your First Encounter with Java Exceptions briefly described how you were (probably) first introduced to Java exceptions: a compiler error complaining that you must either catch or specify exceptions. Then, Java's Catch or Specify Requirement discussed what exactly the error message means and why the Java language designers decided to make this requirement. We're now going to show you both how to catch an exception and how to specify one.

The ListOfNumbers Example

The sections below, both the one on catching an exception and the one on specifying an exception, use the same example. This example defines and implements a class named ListOfNumbers. The ListOfNumbers class calls two methods from classes in the Java packages that can throw exceptions. Catching and Handling Exceptions will show you how to write exception handlers for both exceptions, and Specifying the Exceptions Thrown by a Method will show you how to specify those exceptions instead of catching them.

Catching and Handling Exceptions

Once you've familiarized yourself with the ListOfNumbers class and where the exceptions can be thrown, you can learn how to write exception handlers to catch and handle those exceptions.

This section covers the three components of an exception handler--the try, catch, and finally blocks--by showing you how to use them to write an exception handler for the ListOfNumbers class's writeList method. In addition, this section contains a page that walks through the writeList method and analyzes what occurs within the method during various scenarios.

Specifying the Exceptions Thrown by a Method

If it is not appropriate for your method to catch and handle an exception thrown by a method that it calls, or if your method itself throws its own exception, you must specify in the method signature that the method throws the exception. Using the ListOfNumbers class, this section shows you how to specify exceptions that a method throws.

Handling Errors Using Exceptions