Java Distributed Computing

Making a Thread

The choice between extending the Thread class or implementing the Runnable interface with your application objects is sometimes not an obvious one. It’s also usually not very important. Essentially, the difference between the two classes is that a Thread is supposed to represent how a thread of control runs (its priority level, the name for the thread), and a Runnable defines what a thread runs. In both cases, defining a subclass usually involves implementing the run() method to do whatever work you want done in the separate thread of control.

Most of the time we want to specify what runs in a thread, so in most cases you may want to implement the Runnable interface. With a Runnable subclass, you can use the same object with different types of Thread subclasses, depending on the application. You might use your implementation of Runnable inside a standard Thread in one case, and in another you might run it in a subclass of Thread that sends a notice across the network when it’s started.

On the other hand, directly extending Thread can make your classes slightly easier to use. You just create one of your Thread subclasses and run it, instead of creating a Runnable subclass, putting into another Thread, and running it. Also, if your application objects are subclasses of Thread, then you can access them directly by asking the system for the current thread, or the threads in the current thread group, etc. Then you can cast the object to its subclass and call specialized ...