Question

I’ve getInput method that takes string from text field on enter click. I’ve created while loop to wait until onClickListener returns true (pressed Enter). Here’s my code:

public String getInput(){
    jTextField1.setEditable(true);
    jTextField1.addKeyListener(new java.awt.event.KeyAdapter() {
        public void keyPressed(java.awt.event.KeyEvent evt) {
            temp=jTextField1KeyPressed(evt);
        };
    });
    while(!(temp)){
    }
    temp=false;
    jTextField1.setEditable(false);
    String s= jTextField1.getText();
    jTextField1.setText("");
    return s;

}

private boolean jTextField1KeyPressed(KeyEvent evt) {
    if (evt.getKeyCode() == KeyEvent.VK_ENTER)
        return true;
    else return false;
};

Now I have very strange problem: if I add System.out.println sentence in while loop, it works perfectly, if I remove it, while loop never exits. Where is problem?
Thanks in advance.

Answer 1

You would need some synchronization so that the changes to temp are propagated to all required threads. But it’s a bad approach to start with – getInput will waste a lot of CPU looping in that while for no good purpose.

You could do it more cleanly. First, declare temp to be a java.lang.Object, and initialize it to a plain old Object:

private Object temp = new Object();

(or something like that.)

In getInput, instead of this:

while (!temp) { }
temp = false;

put this:

synchronized (temp) {
  try {
    temp.wait();
  } catch (InterruptedException ie) {
    // handle this situation: something interrupted your thread before input was finished
  }
}

And in the event handler:

synchronized (temp) {
  temp.notify();
}

This way, the thread running getInput stays asleep waiting for something to happen rather than burning CPU cycles.

There are also variants of wait() that take a timeout value. You might be interested in using those too.