Multiple threads with graphical components

[tom davies]

I have a JFrame, within that i have a JPanel that i would like to add a number of balls to, which will each move independently bouncing off the bounding box.
I have managed to get it working with 1 ball and a timer class, but now i am trying to get it to work with threads, so i assign 1 thread to each ball.
At the moment my structure is
BallFrame extends JFrame
BallsPanel extends JPanel
Ball.java extends component
BallRunnable implements runnable

I have added a println into the run method in BallRunnable and that prints out so i know my thread is running it is just not painting my component. Could someone tell me where i have gone wrong.

BallRunnable

import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class BallRunnable implements Runnable 
{
    final static int DIAMETER = 20;
    private Ball newBall;
    private int xCor;
    private int yCor;
    private int speedX;
    private int speedY;
    private int widthBound;
    private int heightBound;
    
    public BallRunnable(Ball aBall, int x, int y, int aSpeedX, int aSpeedY)
    {
        newBall = aBall;
        widthBound = 600;
        heightBound = 400;
        xCor = x;
        yCor = y;
        speedX = aSpeedX;
        speedY = aSpeedY;
        newBall.repaint();
        System.out.println("New Ball");
    }
    
    public void paintComponent(Graphics g)
    {
        paintComponent(g);
        newBall.draw(g);
    }
    
    public void move()
    {
        xCor = xCor + speedX;
        yCor = yCor + speedY;
        
        if(xCor < 0)
        {
            xCor = 0;
            speedX = - speedX;
        } else if(xCor > widthBound)
        {
            xCor = widthBound;
            speedX = - speedX;
        }
        
        if(yCor < 0)
        {
            yCor = 0;
            speedY = - speedY;
        } else if(yCor > heightBound) {
            yCor = heightBound;
            speedY = - speedY;
        }
    }
            
    public void run()
    {   
        while(true)
        {
            System.out.println("Running");
            move();
            newBall.repaint();
        }
        
    }
    
}

Ball

import java.awt.*;
import javax.swing.JComponent;
public class Ball extends JComponent  
{
    final static int DIAMETER = 20;
    private int xCor;
    private int yCor;
    private int speedX;
    private int speedY;
    private int widthBound;
    private int heightBound;
    
    public Ball(int x, int y, int speedx, int speedy)
    {
        xCor = x;
        yCor = y;
        speedX = speedx;
        speedY = speedy;
    }
    
    public void draw(Graphics g)
    {
        g.setColor(Color.red);
        g.fillOval(xCor,yCor, DIAMETER, DIAMETER);
    }

and this is where i add a ball to my JPanel (from my JFrame) and also set the thread for the ball

public void addBall(int x,int y,int speedX, int speedY)
    {
        Ball newBall = new Ball(x,y,speedX,speedY);
        ballpanel.add(newBall);
        
        Runnable r = new BallRunnable(newBall,x,y,speedX,speedY);
        Thread t = new Thread(r);
        t.start();
    }

[Tony Docherty]

I don't understand your BallRunnable class. Why does it have a paintComponent() method when it isn't a GUI component? What is supposed to call this method? Also why does the first line of the method then recursively call itself which can only lead to a stack overflow? Finally the move method changes the x, y values of the BallRunnable object and not of the Ball.

The Ball class has a draw() method which I'm guessing should be paintComponent() as paintComponent() will be called as a result of the BallRunnable object calling repaint() on the Ball.

[tom davies]

This thread can probably be removed as all the classes and structure have been completely changed, thankfully everything is now working though.

[Tony Docherty]

Glad to hear you have it working.
We don't remove threads just because they are resolved as the information here may help someone else in the future.