Even though Wait is called , it is still running the Thread

[Ravi Kiran Va]

Hi ,

Even though i am calling wait , it is still running the Thread .

class Ant extends Thread {
	public void run() {
		System.out.println("Hi i am Ant");
	}
}
public class Test {
	public static void main(String[] args) {
		Ant a = new Ant();
		a.start();
		synchronized (a) {
			try {
				a.wait();
			} catch (Exception e) {
				e.printStackTrace();
			}

		}

	}
}

Any ideas . please advise .

[Stephan van Hulst]

There are a few problems with your code. One, the thread that will display the message has been started before you do any synchronization, and there is a good chance it will print the message before you even get a chance to lock anything. You have made a race condition.

Secondly, you are synchronizing the main thread on the created object. The actual thread you want to wait is not waiting, because it never called wait (only System.out.println()).

Take a look at this example, see if you understand how it works:

class Ant implements Runnable {
    private volatile boolean pause, finish;

    public void run() {
        while (!finish) {
            try {
                System.out.println("Hi I am Ant");
                Thread.sleep(1000);

                synchronized (this) {
                    while(pause) {
                        wait();
                    }
                }
            } catch (InterruptedException ex) {
                ex.printStackTrace();
            }
        }
    }

    synchronized void pause() {
        pause = true;
    }

    synchronized void go() {
        pause = false;
        notifyAll();
    }

    synchronized void finish() {
        finish = true;
    }

    public static void main(String... args) {
        try {
            Ant ant = new Ant();
            new Thread(ant).start();
            Thread.sleep(4500);
            System.out.println("Pausing");
            ant.pause();
            Thread.sleep(3500);
            System.out.println("Continuing");
            ant.go();
            Thread.sleep(4500);
            System.out.println("Finishing");
            ant.finish();
        } catch (InterruptedException ex) {
            ex.printStackTrace();
        }
    }
}

[Javin Paul]

Yes , here the thread which is waiting is Main Thread instead of thread which is printing , to wait the printing thread put wait condition on printing thread instead on main thread.

[Ravi Kiran Va]

Yes , here the thread which is waiting is Main Thread instead of thread which is printing , to wait the printing thread put wait condition on printing thread instead on main thread.

Thanks for the reply , but can you please tell me , how can i put a wait condition on the Printing Thread depending upon on the condition inside the Thread .

any sample piece of code on this please .

[Ravi Kiran Va]

Any body please explain .

[Stephan van Hulst]

Have your printing thread check a variable, and if it's not in the correct state, have it wait. This variable is set by your main thread.
Check the code I posted, it's all in there.