Thread continuing even though it's declared null JAVA

Question

maybe someone can help me- in an applet I declared instances of two threads, started them, and made a "stop" button that declares them null. In the thread classes, I made a while (this != null), and the threads are still running after i hit the button.

Here is the init method of the applet:

public void init(){
    System.out.println("hi");
    setSize(400,200);                                 // make the applet size big enough for our soup bowl
    s = new Soup();                                   // instantiate the Soup
    p1 = new Producer(this, s);              // declare and instantiate one producer thread - state of NEW
    c1 = new Consumer(this, s);              // declare and instantiate one consumer thread - state of NEW
    p1.start();                                       // start the producer thread
    c1.start();                                       // start the consumer thread

    Button stop = new Button("Stop");
    stop.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            p1 = null;
            c1 = null;
            s.getContents().clear();
        }
    });
    add(stop);
}

and here are the run methods of the threads:

public void run() {
    String c;
    try {
        while (this != null) {                           // only put in 10 things so it will stop
            System.out.println("thikns producer != null");
            c = String.valueOf(alphabet.charAt((int)(Math.random() * 26)));   // randomly pick a number to associate with an alphabet letter
            soup.add(c);                                            // add it to the soup
            System.out.println("Added " + c + " to the soup.");     // show what happened in Console
            bowlView.repaint();                                     // show it in the bowl  
            sleep((int)(Math.random() * 2000));  // sleep for a while so it is not too fast to see
        }
    } catch (InterruptedException e) {
        this.interrupt();
    }

}

and this:

  public void run() {
    System.out.println(soup.shouldConsume);
    String c;
    try {
        while(this != null) {              // stop thread when know there are no more coming; here we know there will only be 10
            c = soup.eat();                            // eat it from the soup
            System.out.println("Ate a letter: " + c);  // show what happened in Console
            bowlView.repaint();                        // show it in the bowl  
            sleep((int)(Math.random() * 3000));    // have consumer sleep a little longer or sometimes we never see the alphabets!
        }    
    } catch (InterruptedException e) {
        this.interrupt();
    }

}

any ideas why this is not working? Any input is appreciated! Thanks everyone!

See [this question](http://stackoverflow.com/questions/10961714/how-to-properly-stop-the-thread-in-java) for how to stop a thread in java — dnault, May 14 '15 at 01:08
Why would `p1 = null` stop the thread? `p1` isn't the thread, it's a field containing a reference to the thread. — user253751, May 14 '15 at 01:09
to immbis- so then how would i stop the whole thread? interrupt is not static, so I can't call it with the class name either — TryingToCode, May 14 '15 at 22:09

score 1 · Answer 1 · answered May 14 '15 at 01:13

1

while (this != null) can never be false.

Setting another reference to the thread to null neither stops the thread nor causes its this to become null.

Your code doesn't make sense.

[The Java magazines of the late 1990s were full of while (Thread.currentThread() == this) tests. That made no sense either.]

answered May 14 '15 at 01:13

user207421

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Thanks! I'm pretty new to this, as you can see :) When I tried to do this: Button stop = new Button("Stop"); stop.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { p1.interrupt(); c1.interrupt(); s.getContents().clear(); } }); add(stop); , it did not work either. – TryingToCode May 14 '15 at 01:36
`Thread.interrupt()` only interrupts methods that can throw `InterruptedException`. For all other code it just sets the `Thread.isInterrupted()` status. So if you want to use `interrupt()` the code in the thread has to co-operate, by exiting if `InterruptedException` is caught, and by polling `isInterrupted()` regularly. Most code doesn't do either of those things. – user207421 May 14 '15 at 03:07

Thread continuing even though it's declared null JAVA

1 Answers1