Special Edition Using Java 2 Standard Edition

Implementing Runnable

The second way to cause classes to behave as threads is to have those classes implement the java.lang.Runnable interface. A second method is available because extending the Thread class will not work in all cases. This is because Java does not allow for a class to be a subclass of more than one direct parent class. Other languages such as C++ do allow this, but Java does not. For example, the SimpleThread class shown previously could not extend Thread and Date classes simultaneously.

If you need to create a new class that acts as a thread and this new class already extends a different class, the alternative is to have the new class implement the Java Runnable interface instead. The Runnable interface defines a single interface ...