Ivor Horton's Beginning Java™ 2, JDK™ 5th Edition

7.1. The Idea Behind Exceptions

An exception usually signals an error and is so called because errors in your Java programs are bound to be the exception rather than the rule—by definition! An exception doesn't always indicate an error though—it can also signal some particularly unusual event in your program that deserves special attention.

If you try to deal with the myriad and often highly unusual error conditions that might arise in the midst of the code that deals with the normal operation of the program, your program structure will soon become very complicated and difficult to understand. One major benefit of having an error signaled by an exception is that it separates the code that deals with errors from the code that is executed when things are moving along smoothly. Another positive aspect of exceptions is that they provide a way of enforcing a response to particular errors. With many kinds of exceptions, you must include code in your program to deal with them; otherwise, your code will not compile.

One important idea to grasp is that not all errors in your programs need to be signaled by exceptions. Exceptions should be reserved for the unusual or catastrophic situations that can arise. A user entering incorrect input to your program for instance is a normal event and should be handled without recourse to exceptions. The reason for this is that dealing with exceptions involves quite a lot of processing overhead, so if your program is handling exceptions a lot of the ...