While loop not working unless I insert a print statement - java

LightningdeGolem :

I am writing a GUI for a program which allows a user to accept or decline a request send to a listening server socket. I do this by using a DoYouAcceptWindow and another bit of code which opens it.

The code in DoYouAcceptWindow.java is as follows

public class DoYouAcceptWindow extends JFrame implements MouseListener{
    private short d = 0;
    private JButton accept;

    public DoYouAcceptWindow() {
        setLayout(new FlowLayout());
        accept = new JButton("Accept");
        accept.addMouseListener(this);
        add(accept);

        pack();
        setVisible(true);
    }

    public short getDecided() {
        return d;
    }

    @Override
    public void mouseClicked(MouseEvent e) {
        if (e.getSource().equals(accept)) {
            System.out.println("Accepted");
            d = 2;
        }
    }
}

(I have remove a lot of unnecessary functions from this as well as the ability to decline the request just to make it easier to read)

And the code that uses the above class:

while (true) {
    DoYouAcceptWindow w = new DoYouAcceptWindow();
    short decided = w.getDecided();
    while (decided == 0) {
        decided = w.getDecided();
    }
    System.out.println("Done!");
    w.dispose();
    if (w.getDecided() == 2) {
        break;
    }
}

(This code has also had a lot of unnecessary parts removed)

When you press the button, it prints "accepted" like it should (and I assume it sets d = 1 or 2). However, it does not break out of the while loop. When I add a print statement into the while loop however (like this):

while (decided == 0) {
    decided = w.getDecided();
    System.out.println(0);
}

It fixes itself. If I run it in debug mode (in eclipse), it fixes itself. Why does it not break out of the while loop without the print statement? And how can I fix it? (without adding a print statement)

Roland Kreuzer :

Can't say for sure, but with the description this could be a memory visibility issue.

Could you try declaring the value volatile?

private volatile short d = 0;