Java uses exceptions as a way of signaling serious problems when you execute a program. The standard classes use them extensively. Since they arise in your Java programs when things go wrong, and if something can go wrong in your code, sooner or later it will, they are a very basic consideration when you are designing and writing your programs.
The reason we've been sidestepping the question of exceptions for the past six chapters is that you first needed to understand classes and inheritance before you could understand what an exception is, and appreciate what happens when an exception occurs. Now that you have a good grasp of these topics we can delve into how to use and deal with exceptions in a program.
In this chapter you will learn:
What an exception is
How you handle exceptions in your programs
The standard exceptions in Java
How to guarantee that a particular block of code in a method will always be executed
How to define and use your own types of exceptions
How to throw exceptions in your programs