Question

This post relates to my last one regarding a timer. I decided the easiest thing to do for immediate results was to just write a Counter thread that counts down from a certain time (in this case 5 seconds) and if the counter reaches 0, the JFrame closes and let’s the user know that time has expired.

I’m running into some trouble, however. I cannot seem to make the JFrame close when the counter reaches 0. I’m not sure if I’m missing something stupid or if I am misunderstanding the way threads work and the way JFrames work. Here is the code, let me know what you think.

On a side note, I understand it would probably be most efficient to use a swing.Timer, but I just don’t quite grasp the nature of them yet. I’m under self-imposed time constraints (I’m not a student or anything, I just like to stay motivated) and so I’m “jerry-rigging” this thing for now.

Anyway, on to the code!

import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;

public class RacerDoom extends JFrame {

boolean timesUp=false;

public RacerDoom() {
//create JFrame
super("Racer Doom Squared");
setSize(WIDTH,HEIGHT);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setVisible(true);
if(timesUp==true) {
dispose();
JOptionPane.showConfirmDialog(null, "Time's Up! Click Okay to try again!");
}

Counter c1 = new Counter();
c1.start();

//Counter
private class Counter extends Thread {
public Counter() {}
public void run() {
for(int i=5;i>=0;i--) {
if(i==0) {
timesUp=true;
}
System.out.println(i);
try{
Thread.sleep(1000);
}
catch(InterruptedException e){}
}
}
}
...

EDIT: I have the timer implemented and working. It does exactly what I need it to, but I can’t get the timer.stop(); command to work. I get the error “The local variable timer may not have been initialized.

Like I said, the timer works, it just never stops working until the program is terminated. Here is the constructor code for the JFrame, where the timer is located.

int counter = 0;

public RacerDoom() {
    //create JFrame
    super("Racer Doom Squared");
    setSize(WIDTH,HEIGHT);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setVisible(true);
    final Timer timer=new Timer(1000, new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            if(counter>=10) {
                timer.stop();  //the error occurs here
                dispose();
                JOptionPane.showConfirmDialog(null, "Time's Up!");
            }
            else{
               counter++;
               }
            System.out.println(counter);
        }
    });

    //inner thread
    Move1 m1 = new Move1();
    m1.start();

    timer.start();
    }

Answer 1

Thats easy to do with the help of a swing timer.. See this code sample:

final java.swing.Timer timer=new Timer(1000, new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            if(counter>5) {
                timer.stop();
                <dispose the fram here>
            }else{
               counter++;
               }
        }
    });
    timer.start();

I put this code in the constructor of my JFrame which will run in the Event despatch thread. If you dont want hang up your GUI, make sure that you run this timer on another thread and when you are disposing the JFrame wrap the call with SwingUtilities.invokeLater() – This ensures that the call gets queued on the event despatch thread.

I think your code is not working for the same reason, that you trying to something that does not get queued up in the event despatch thread. Here’s an article that will get you going

http://java.sun.com/products/jfc/tsc/articles/threads/threads1.html