Java Multiple Threads Demo not Working

Question

I'm writing a small program to see how multiple threads can be run in Java. Not sure why I'm not getting any output:

class NuThread implements Runnable {
    NuThread() {
        Thread t = new Thread(this, "NuThread");
        t.start();
    }

    public void run() {
        try {
                for (int i=0; i<5; i++) {
                Thread th = Thread.currentThread();
                System.out.println(th.getName() + ": " + i);
                Thread.sleep(300);
            }
        } catch (InterruptedException e) {
            Thread th = Thread.currentThread();
            System.out.println(th.getName() + " interrupted.");
        }
    }
}

public class MultiThreadDemo {
    public static void main(String[] args) {
        NuThread t1, t2, t3;
        try {
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            System.out.println("Main interrupted.");
        }   
    }
}

score 1 · Answer 1 · edited May 23 '17 at 10:33

1

You are not creating object of NuThread. That's why thread is not starting.

And it's not the best idea to start thread in the constructor, see here.

edited May 23 '17 at 10:33

Community

1
1

answered Nov 22 '14 at 17:16

Maksym

4,434
4
27
46

score 1 · Accepted Answer · answered Nov 22 '14 at 17:16

You're not creating any instances of NuThread. This line:

NuThread t1, t2, t3;

... just declares three variables. It doesn't create any instances. You'd need something like:

NuThread t1 = new NuThread();
NuThread t2 = new NuThread();
NuThread t3 = new NuThread();

Having said that, making a constructor start a new thread is a little odd in itself... it might be better to remove that and just have:

// TODO: Rename NuThread to something more suitable :)
NuThread runnable = new NuThread();
Thread t1 = new Thread(runnable);
Thread t2 = new Thread(runnable);
Thread t3 = new Thread(runnable);
t1.start();
t2.start();
t3.start();

Note that it's okay to use the same Runnable for all three threads, as they don't actually use any state.

Thanks! This is how threads are created in Herbert Schildt's book, although I do feel that you have a point. Something else (main?) should be creating and running threads. — ankush981, Nov 22 '14 at 17:19

Java Multiple Threads Demo not Working

2 Answers2