Q on Threads

[priti manas duddilla]

Given:

11. Runnable r = new Runnable() {
12. public void run() {
13. System.out.print(�Cat�);
14. }
15. };
16. Threadt=new Thread(r) {
17. public void run() {
18. System.out.print(�Dog�);
19. }
20. };
21. t.start();

What is the result?
A. Cat
B. Dog
C. Compilation fails.
D. The code runs with no output.
E. An exception is thrown at runtime.

Answer: B
Can some one please clarify,
Runnable is the job and Thread is the worker(a line directly quoted from K&B).
So in the above example, i have given a job(runnable) to thread(worker), then doesn't the thread execute runnable's run method?

[ahmed yehia]

Thread implements Runnable, so at runtime run() in Thread is executed.
correct me if I m wrong

[marc weber]

Originally posted by Ahmed Yehia:
Thread implements Runnable, so at runtime run() in Thread is executed...

That's true, but if the Thread was constructed using a separate Runnable, then the implementation of Thread's run method is to invoke the Runnable's run method.
[ September 25, 2007: Message edited by: marc weber ]

[marc weber]

If "t" were just an instance of Thread, then its own run method would invoke the Runnable's run method, and you would get the behavior you expected. However, in this example, "t" is a subclass of Thread, and its run method has been overridden so that it does not invoke the Runnable's run method.

If you still want the overridden run method to invoke the Runnable's run method, then you could call super.run() to get the superclass behavior...

class TestRunnable {
  public static void main(String[] args) {
    Runnable r = new Runnable() {
      public void run() {
        System.out.println("Cat");
      }
    };
    Thread t = new Thread(r) {
      public void run() {
        [B]super.run();[/B]
        System.out.println("Dog");
      }
    };
    t.start();
  }
}