Why is run() getting called just once?

Question

Consider this class, AnimationThread:

class AnimationThread implements Runnable {
    public void pause() {
        doAnimation = false;
    }

    public void doStart(){
        doAnimation = true;
    }

    @Override
    public void run() {
        // TODO Auto-generated method stub
        if (doAnimation) {
            //my code
        }

        try {
            Thread.sleep(500);
        } 
        catch (InterruptedException e) {

        }
    }
}

Now I am starting this thread in onCreate of an activity (just showing rough code):

AnimationThread animRunnable = new AnimationThread();
animationThread = new Thread(animRunnable);
animationThread.start();

But run() is getting called just once (I traced a log to confirm that). I just want to know that when I started the thread why run() is not getting called repeatedly with 500 sleep. It is just called once.

score 12 · Accepted Answer · answered Nov 18 '11 at 05:11

12

That is how it is supposed to be.

A Thread runs by executing its run method (just once). After that it is considered done/dead/finished/completed.

If you want to loop, you have to do it yourself (inside of the run method), or use some ExecutorService to call the Runnable repeatedly.

answered Nov 18 '11 at 05:11

Thilo

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Thanks. I got the logic. I am making sure inside run my logic code is running repeatedly. Actually in my situation i want run() to execute infinetly for my purpose so i have enclosed my logic within while(true) inside run and animation occurs based on state of doAnimation state variable. Thanks. – padam thapa Nov 18 '11 at 05:28
That is a common pattern. However, you probably want the thread to terminate eventually in order to shutdown the program. Or you could use a daemon thread for that. – Thilo Nov 18 '11 at 06:36

score 8 · Answer 2 · edited May 23 '17 at 11:52

8

Of course the run() method will be executed once. If you want to repeat the statements inside the run method then you have to use loop. Take a look at TimerTask - will runs a task at a specified time or repeatedly.

EDIT:

edited May 23 '17 at 11:52

Community

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1

answered Nov 18 '11 at 05:10

KV Prajapati

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Why is run() getting called just once?

2 Answers2