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Thread: Need Help Getting A Simple Stop-Watch Working?

  1. #1
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    Unhappy Need Help Getting A Simple Stop-Watch Working?

    So I am experimenting with a little stop-watch object and I can't figure out why it isn't working. I have a gui with the following;
    timeinfield is a jtextfield which the user enters the start time of the clock.
    timerfield is a jtextfield where the clock is displayed timing.
    startbutton is a jbutton where the user clicks to start the clock.
    stopbutton is a jbutton where the user clicks to stop the clock.

    I want the clock to look like 00.00.00 and keep updating until the user clicks stop. Then I am going to do something with the stop value later on.

    Right now, the timerfield just displays Running: 0 seconds.
    Nothing else happens, maybe I am doing this wrong for it is my first time trying something like this. I am about to start learning how to use threads so I thought this might help get me started.

    Could someone help me write something like this that corresponds to the buttons and areas I have above? This is what I have so far;
        private void startbuttonActionPerformed(java.awt.event.ActionEvent evt) {
     
                String starttim = timeinfield.getText();
                long startTime = Long.valueOf(starttim);
                boolean running = false;
                Timer timer = null;
                timer.stop();
                long time = (System.currentTimeMillis() - startTime)/1000;
     
                timerfield.setText("Running:" + time + "seconds");
                if(running==false){
                running = true;
                timerfield.setText("Running: 0 seconds");
     
                                    }
                if(stopbutton.isSelected()) {
                timer.stop();
                running = false;
                long endTime = evt.getWhen();
                double seconds = (endTime - startTime)/1000.0;
                timerfield.setText("Time: " + seconds + "sec.");
                }
    // going to need timer.stop() while timer is null or null pointer exception occurr
     
        }


  2. #2
    Crazy Cat Lady KevinWorkman's Avatar
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    Default Re: Need Help Getting A Simple Stop-Watch Working?

    You declare timer but initialize it to null. What do you expect to happen? This is going to cause a NullPointerException every time.
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