Java™ How To Program (Early Objects), Tenth Edition

11.9 Declaring New Exception Types

Most Java programmers use existing classes from the Java API, third-party vendors and freely available class libraries (usually downloadable from the Internet) to build Java applications. The methods of those classes typically are declared to throw appropriate exceptions when problems occur. You write code that processes these existing exceptions to make your programs more robust.

If you build classes that other programmers will use, it’s often appropriate to declare your own exception classes that are specific to the problems that can occur when another programmer uses your reusable classes.