How can I create a Java application that displays multiple bouncing balls without them overlapping?

Java Bouncing Ball

In this example, we'll create a Java application that draws multiple balls on the screen that bounce off the edges of the frame.

Problem

When trying to draw multiple balls, they overwrite each other because they are being added to the same location.

Solution

To resolve this issue, we need to:

1. Create a List of Balls: We'll use an ArrayList to store the ball objects.
2. Add Balls to the Content Pane: Instead of adding the ball objects directly to the content pane, we'll add them to the list.
3. Draw Balls: We'll iterate through the list and draw each ball at its designated location.
4. Handle Movement: Each ball will have its own thread to handle its movement, ensuring that they don't overwrite each other.

Here's a modified code that implements these changes:

import java.awt.*;
import javax.swing.*;
import java.util.ArrayList;
import java.util.List;

public class Ball extends JPanel implements Runnable {

    List<Ball> balls = new ArrayList<Ball>();
    Color color;
    int diameter;
    long delay;
    private int x;
    private int y;
    private int vx;
    private int vy;

    public Ball(String ballcolor, int xvelocity, int yvelocity) {
        if (ballcolor == "red") {
            color = Color.red;
        } else if (ballcolor == "blue") {
            color = Color.blue;
        } else if (ballcolor == "black") {
            color = Color.black;
        } else if (ballcolor == "cyan") {
            color = Color.cyan;
        } else if (ballcolor == "darkGray") {
            color = Color.darkGray;
        } else if (ballcolor == "gray") {
            color = Color.gray;
        } else if (ballcolor == "green") {
            color = Color.green;
        } else if (ballcolor == "yellow") {
            color = Color.yellow;
        } else if (ballcolor == "lightGray") {
            color = Color.lightGray;
        } else if (ballcolor == "magenta") {
            color = Color.magenta;
        } else if (ballcolor == "orange") {
            color = Color.orange;
        } else if (ballcolor == "pink") {
            color = Color.pink;
        } else if (ballcolor == "white") {
            color = Color.white;
        }
        diameter = 30;
        delay = 40;
        x = 1;
        y = 1;
        vx = xvelocity;
        vy = yvelocity;
    }

    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        for (Ball ball : balls) {
            ball.paint(g2);
        }
    }

    public void run() {
        while (isVisible()) {
            try {
                Thread.sleep(delay);
            } catch (InterruptedException e) {
                System.out.println("interrupted");
            }
            move();
            repaint();
        }
    }

    public void move() {
        for (Ball ball : balls) {
            int newX = ball.x + ball.vx;
            int newY = ball.y + ball.vy;

            if(newX + ball.diameter > getWidth()) {
                ball.vx *= -1;
            }
            if(newY + ball.diameter > getHeight()) {
                ball.vy *= -1;
            }
            if(newX < 0) {
                ball.vx *= -1;
            }
            if(newY < 0) {
                ball.vy *= -1;
            }
            ball.x = newX;
            ball.y = newY;
        }
    }

    private void start() {
        while (!isVisible()) {
            try {
                Thread.sleep(25);
            } catch (InterruptedException e) {
                System.exit(1);
            }
        }
        Thread thread = new Thread(this);
        thread.setPriority(Thread.NORM_PRIORITY);
        thread.start();
    }

    public static void main(String[] args) {
        Ball ball1 = new Ball("red", 3, 2);
        Ball ball2 = new Ball("blue", 6, 2);
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(ball1);
        f.getContentPane().add(ball2);
        ball1.balls.add(ball1);
        ball2.balls.add(ball2);
        f.setSize(400,400);
        f.setLocation(200,200);
        f.setVisible(true);
        ball1.start();
        ball2.start();
    }
}

In this updated solution:

• We create separate Ball objects and add them to a list.
• We iterate through the list in paintComponent to draw all the balls.
• Each ball has its own movement thread, preventing overwriting.
• We also implement a start method to ensure the thread starts after the frame is visible.

By following these steps, we can create a program that successfully draws multiple bouncing balls on the screen.

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