Thread: MouseListener accumulating mouse clicks

Hi there,

I am writing a basic GUI that has a circle in it and when you click the circle it cycles through a choice of 4 colours.

I have written a class that extends JPanel and uses paintComponent to draw the circle, I then use this in another class as an object in a JFrame.

To change the colour of the circle I have used a MouseListener, and a modulus function, however when you click the first time the MouseListener calls the code inside of it once, but the second time it calls the code twice and the third 3 times and so on.

Please help as I can't see why it would do this, below is the code for the JPanel class

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
 
public class CircleClicker extends JPanel{
 
	public final static int RED = 1, YELLOW = 2, GREEN = 3, BLUE = 0;
	int colour = 0;
 
	public void paintComponent(Graphics g){
 
		super.paintComponent(g);
 
		addMouseListener(
			new MouseAdapter(){
				public void mousePressed(MouseEvent e){
					colour = (colour + 1);
					repaint();
					System.out.println("Click value " + colour);
				}
			}
		);
 
		if (colour==RED){
			g.setColor(Color.RED);
			//g.fillOval(100, 100, 50, 50);
		}
		else if (colour==YELLOW){
			g.setColor(Color.YELLOW);
			//g.fillOval(100, 100, 50, 50);
		}
		else if (colour==GREEN){
			g.setColor(Color.GREEN);
			//g.fillOval(100, 100, 50, 50);
		}
		else if (colour==BLUE){
			g.setColor(Color.BLUE);
			//g.fillOval(100, 100, 50, 50);
		}
		else{
			g.setColor(Color.lightGray);
		}
		g.fillOval(0,0,50,50);
	}
 
	public Dimension getPreferredSize(){
		return new Dimension(50, 50);
	}
 
	public Dimension getMinimumSize(){
		return getPreferredSize();
	}
}

Question: Why is your mouse listener inside of your paintComponent method?

The most obvious way would be to create a constructor for CircleClicker and put the statement to add the mouse listener in there. I don't know of any way to add a mouse listener by overriding anything.

To make sure that CircleClicker is still technically a JPanel, you want to call the JPanel constructor as your first statement in your constructor. To do this, use the following statement: super();

Since your problem isn't directly about constructors and I would have to assume that you understand constructors since you are doing listeners, I'll provide you the code for the constructor since it is really just reorganizing your code:

public CircleClicker()
{
	super();
	addMouseListener(
            new MouseAdapter(){
                public void mousePressed(MouseEvent e){
                    colour = (colour + 1);
                    repaint();
                    System.out.println("Click value " + colour);
                }
            }
        );
}

Remember to also remove the mouse listener from your paintComponent method.