Throwing Exceptions

• Java allows you to have an alternate exit path if a method malfunctions.
• Instead of simply returning a number or other return value that represents an error code, you can send back more information.
• The alternate path throws an exception.  An Exception is an object that encapsulates error information.
• When an exception is thrown, the program skips all code until it finds an exception handler that is built to deal with that exception.
• There are different types of Exceptions, each of which extends class Exception.
• Exception extends class Throwable.
• IOException, ParseException, etc.  These are all linked on the Exception API documentation.
• You can even create your own Exception subclasses.  Used properly, these can be very powerful!
• Each exception type can have its own handler.
• On a high level, we can group exceptions into two types:
• Those that extend RuntimeException and those that do not.
• Generally, RuntimeExceptions are errors that occur due to programming problems, such as bad casts, trying to reach an array element that does not exist, and null pointers..
• Other errors are not controlled by the program, such as an IO error.  These include attempting to read past the end of a file, attempting to open an incorrect URL, and trying to instantiate a class dynamically that does not exist.
• Class Error also extends Throwable, but these are generally internal errors.  You shouldn't throw or catch these.

Created by:  Brandan Jones December 17, 2001