Overview

Chapter 12 - Exception Callback Java Thread Programming Paul Hyde

size=1>  size=2>Copyright � 1999 Sams Publishing

size=5>Chapter 12: size=5>Exception Callback

size=4>Overview

size=2>Exceptions can be thrown just about anywhere in a Java program. Methods must declare all of the exceptions they might throw except for size=2>RuntimeException and its subclasses. A size=2>RuntimeException can occur on just about every line of code (just think of the fact that size=2>NullPointerException size=2> can be thrown anytime a method is invoked if the object reference s size=2>nullsize=2>!).

size=2>When an exception occurs and is not immediately caught, it propagates up the call stack until it either is caught by one of the invoking methods, or remains uncaught. For methods called from the size=2>main() method, the exception can potentially float all the way back up to size=2>main() and get reported there. However, when a new thread is spawned, a brand new call stack is created. This call stack starts with the color=#010100 face="Courier New" size=2>run() color=#010100 face=Arial size=2> method. The color=#010100 face="Courier New" size=2>run() color=#010100 face=Arial size=2> method does not declare that it throws any exceptions and should therefore catch all of them.

size=2>Many times Java developers are frustrated by the fact that they cannot catch exceptions that occur in other threads. In this chapter, I’ll show you a way to pass exceptions that occur inside an active class to another class to signal it that a potential problem has occurred.

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