Timer/Stopwatch GUI

Question

I am trying to make a simple java application that counts time, with the ability to stop and start the timer. However, the label won't update, and when I press start, it freezes.

Could you help me figure out what the problem is?

package random;

import javax.swing.JFrame;

public class Timer {
boolean shouldCount=false;
int int_sec=0;
int int_min=0;
int int_mil=0;
public static void main(String[] args) {
    TimeFrame t = new TimeFrame();
    JFrame f = new JFrame("Timer");
    f.setSize(300,200);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.setLocationRelativeTo(null);
    f.getContentPane().add(t);
    f.setVisible(true);
}

public void count(){
    TimeFrame t = new TimeFrame();
    if(shouldCount){
        long now = System.currentTimeMillis();
        while(true){
            if(System.currentTimeMillis()-now>=100){
                now=System.currentTimeMillis();
                String sec = Integer.toString(int_sec);
                String min = Integer.toString(int_min);
                String mil = Integer.toString(int_mil);
                t.update(sec,int_sec,min,mil,int_mil);
                int_mil++;
                if(int_mil>9){
                    int_mil=0;
                    int_sec++;
                    if(int_sec>=60){
                        int_sec=1;
                        int_min++;
                    }
                }
            }
        }
    }
}
}

And here is TimeFrame.java

    package random;

    import java.awt.event.ActionEvent;
    import java.awt.event.ActionListener;
    import javax.swing.JButton;
    import javax.swing.JLabel;
    import javax.swing.JPanel;

    public class TimeFrame extends JPanel{
    JLabel time = new JLabel("Time goes here", JLabel.CENTER);
    Timer t = new Timer();
    JButton pause = new JButton ("Pause");
     JButton start = new JButton ("Start");
    public TimeFrame(){

         start.addActionListener(new starts());
         pause.addActionListener(new starts());
         add(time);
         add(start);
         add(pause);
    }
    public void update(String sec,int s, String min,String mil,int m){
        if (s<=10){
            sec="0"+sec;
        }
        System.out.println(min+":"+sec+","+mil);
        time.setText(min+":"+sec+","+mil);

    }
    public class starts implements ActionListener{
        public void actionPerformed(ActionEvent event){
            if(event.getSource() == start){
                t.shouldCount=true;
            }else{
                t.shouldCount=false;
            }
            t.count();
        }
    }
}

Answer 1

The problem is that you have only one thread in your application. You should have at least two : one for the UI that will update the text and one for the computation of the time.

If you have only one thread it hangs in the while(true) loop and Swing never get to update the view.

I refactored your code using two threads :

1. One counting until the end of time and updating the fields to keep time in memory

2. Another one that uses a java.util.Timer#scheduleAtFixedRate() method wich is invoqued every 100 millisec to update the view.

Timer.java (avoid naming classes like ones in the Java API)

    public class Timer {

        boolean shouldCount=false;
        int int_sec=0;
        int int_min=0;
        int int_mil=0;

        public Timer() {
        }

        public static void main(String[] args) {
            TimeFrame t = new TimeFrame();
            JFrame f = new JFrame("Timer");
            f.setSize(300,200);
            f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            f.setLocationRelativeTo(null);
            f.getContentPane().add(new TimeFrame());
            f.setVisible(true);
        }

        public void count(){
                Thread thread = new Thread(new Runnable() {
                    @Override
                    public void run() {
                        long now = System.currentTimeMillis();
                        while(true){
                        if(shouldCount){
                            if(System.currentTimeMillis()-now>=100){
                                now=System.currentTimeMillis();
                                int_mil++;
                                if(int_mil>9){
                                     int_mil=0;
                                     int_sec++;
                                     if(int_sec>=60){
                                          int_sec=1;
                                          int_min++;
                                     }
                                }
                            }       
                        }
                    }               
                }
            });
            thread.start();
        }
    }
}

TimeFrame (I would rather call it TimePanel since it extends JPanel)

public class TimeFrame extends JPanel{
    JLabel time;
    Timer t ;
    JButton pause ;
    JButton start ;
    public TimeFrame(){

        t= new Timer(this);

        time = new JLabel("Time goes here", JLabel.CENTER);
        pause = new JButton ("Pause");
        start = new JButton ("Start");

        start.addActionListener(new starts());
        pause.addActionListener(new starts());
        add(time);
        add(start);
        add(pause);

        java.util.Timer updateTimer= new java.util.Timer();
        updateTimer.scheduleAtFixedRate(new TimerTask() {
        @Override
        public void run() {
            t.update(int_sec,int_min,int_mil);
        }
        }, 0, 100);
    }    

    public void update(int s, int minute,int m){
        String sec = Integer.toString(s);
        String min = Integer.toString(minute);
        String mil = Integer.toString(m);
    if (s<=10){
            sec="0"+sec;
        }

        System.out.println(min+":"+sec+","+mil);
        time.setText(min+":"+sec+","+mil);
    }


   public class starts implements ActionListener{
    boolean firstTime=true;
    public void actionPerformed(ActionEvent event){
        if (firstTime){
            t.count();
            firstTime = false;
        }
        if(event.getSource() == start){
            t.shouldCount=true;
        }else{
            t.shouldCount=false;
        }
    }
}

}