CODEWITHSUNDEEP
javaswingtimerpausing-execution
Falsoon
Falsoon

Reputation: 1129

How to pause the main Swing thread until after a Swing Timer finishes?

I use a Swing.Timer to slow my animation. However, I want to pause my current execution until after the Timer thread completes. How do I do that? The Timer spawns off a new thread that is not responsive to the original. Here is a sample program that demonstrates.

public class TimerFrame extends JFrame
{
  public static void main(String[] args)
  {
    EventQueue.invokeLater(new Runnable() {
      @Override
      public void run()
      {
        TimerFrame frame = new TimerFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);

        TimeListener listener = new TimeListener();
        Timer timer = new Timer(1000, listener);
        timer.start();
        System.out.println("Timer running: " + timer);

        while (!timer.isRunning()) {
          System.out.println("Timer not running: " + timer);
          JOptionPane.showMessageDialog(null, "Quit program?");
          Calendar cal = Calendar.getInstance();
          System.out.println("main pgm: " + cal.getTimeInMillis());
        }
        System.exit(0);
      }
    });
  }
}

class TimeListener implements ActionListener
{
  static int _counter;

  public TimeListener()
  {
    _counter = 1;
  }

  @Override
  public void actionPerformed(ActionEvent e)
  {
    if (_counter <= 3) {
      String msg = "Timer: Counter = " + _counter + " " + e.getWhen();
      JOptionPane.showMessageDialog(null, msg);
      System.out.println(msg);
      _counter++;
    }

    else {
      Timer timer = (Timer) e.getSource();
      timer.stop();
      if (timer.isRunning()) {
        System.out.println("Timer.aP is still running after a stop request");
      }
      else {
        System.out.println("Timer.aP just stopped timer");
      }
    }
  }

}

Note that the timer continues to run even though actionPerformed stops it. After three OptionPane appearances, the program never quits. I expected that the isRunnable() test would be false when the timer completes. The output is

Timer running: javax.swing.Timer@2eb9b326
Timer: Counter = 1 1606837382597
Timer: Counter = 2 1606837385600
Timer: Counter = 3 1606837386601
Timer.aP just stopped timer

Upvotes: 0

Views: 202

Answers (1)

Falsoon
Falsoon

Reputation: 1129

I wrote a few test programs and found a way: Put a flag into the Listener class to true when the timer stops, and a getter to return the state of the flag. The calling program loops until the timeer is completed. Here is the Listener code.

class TimeListener implements ActionListener
{
  static int _counter;
  boolean _endTimer;

  public TimeListener()
  {
    _counter = 1;
    _endTimer = false;
  }

  boolean isTimerDone()
  {
    return _endTimer;
  }


  @Override
  public void actionPerformed(ActionEvent e)
  {
    if (_counter <= 3) {
      String msg = "Timer: Counter = " + _counter + " " + e.getWhen();
      JOptionPane.showMessageDialog(null, msg);
      System.out.println(msg);
      _counter++;
    }

    else {
      Timer timer = (Timer) e.getSource();
      timer.stop();
      _endTimer = true;
    }
  }
}

In the calling program (the one waiting for the timer to end), use a loop to check until the timer is done:

TimeListener listener = new TimeListener();
Timer timer = new Timer(1000, listener);
timer.start();

// Wait until the timer completes
while (listener.isTimerDone());

// continue code here...

Upvotes: 1

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