Replacing an image once through timer

Question

I am working on this reaction time game that tells you to click an arrow key once the ball has turned into a different colored ball. However, I can't seem to get the image of the ball to be replaced by the other ball.

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.Random;
import javax.swing.Timer;

public class Game extends JPanel
{
  private JLabel watch, main;
  private ImageIcon constant, react;
  final int width = 600;
  final int height = 600;
  private Timer replace;
  private ActionListener timerListener;
  
  
  public Game()
  {
    setPreferredSize(new Dimension(width, height));
    setBackground(Color.black);
    
    watch = new JLabel("Click Up Arrow when you see a blue ball");
    watch.setForeground(Color.white);
    add(watch);
   
    constant = new ImageIcon("constantCircle.png");
    main = new JLabel(constant);
    
    replace = new Timer(3000, timerListener);
    replace.setRepeats(false);
    replace.start();
 
    add(main);
    
  }
  
  
  public void actionPerformed (ActionEvent e)
  {
    react = new ImageIcon("reactCircle.png");
    main.setIcon(react);
    
  }
}

This is the code for my display and I wanted to use a swing timer to replace the image after 3 seconds

This is what I want it to look like before

and this is what I want it to look like after 3 seconds

For better help sooner post a proper [mre], where's your `timerListener`? — Frakcool, May 18 '21 at 13:49
I just edited the code to show all my code to show you where the timerListener is. Also, I would try to minimize the amount of code but I honestly don't really know where the problem specifically is. I think its in the timer but I'm just not sure what to do to replace the image with a new one @Frakcool — Zenzu, May 18 '21 at 14:37
Where are you initializing the `timerListener`? So far your `actionPerformed` doesn't belong to anything. Take [this answer](https://stackoverflow.com/a/34748083/2180785) as a starting point. In your current code `replace = new Timer(3000, timerListener);` is the same as `replace = new Timer(3000, null);` — Frakcool, May 18 '21 at 14:39
ohhhhh, okay thank you so much. I just did that and it worked! Thank you @Frakcool — Zenzu, May 18 '21 at 14:44

Frakcool · Accepted Answer · 2021-05-18T15:38:22.357

You're never initializing timerListener

private ActionListener timerListener;

Inside your constructor you have to call (With Java 8 lambdas):

timerListener = e -> {
    react = new ImageIcon("reactCircle.png");
    main.setIcon(react);
}

Or (Java 7 and lower):

timerListener = new ActionListener() {
    @Override
    public void actionPerformed(ActionEvent e) {
        react = new ImageIcon("reactCircle.png");
        main.setIcon(react);
    }
}

~~And don't forget to call timerListener.stop() once the timer has fired, so that you don't keep computing more times~~

From Andrew Thompson's comment below:

As you only want to replace the image once, call timerListener.setRepeats(false) on your constructor. Check the docs for more information about it.

Replacing an image once through timer

1 Answers1