[Pong] Bouncing ball problem

Newbie & Debugging Questions
#1

Hey guys, I’m pretty much new to the Java Graphics part, and I have a couple questions as well.
Anyway, I was trying create a Pong game , and I’m already having some trouble with the ball moving part.
I don’t understand why isn’t the ball moving at all, all it does is flicker in the same place.
I usually extend JComponent in a class, and draw everything inside the paintComponent() method, so I just wanted to try something new I read, but yeah I just cant figure out what am I doing wrong ???

public class GUI {
	JFrame frame;
	Ball ball = new Ball();
	GamePanel gamepanel = new GamePanel();
	BallEngine engine = new BallEngine(gamepanel);

	public GUI() {
		frame = new JFrame("Pong");
		frame.add(gamepanel);
		frame.setSize(400, 400);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	}

	private void execute() {
		frame.setVisible(true);
		engine.start();
	}

	public static void main(String[] args) {
		GUI gui = new GUI();
		gui.execute();
	}
}


public class GamePanel extends JPanel {

	private static final long serialVersionUID = 1L;
	Ball ball = new Ball();
	Paddle paddle = new Paddle();

	public void paintComponent(Graphics g) {
		super.paintComponent(g);
		ball.paintBall(g);
		paddle.paintPaddle(g);
	}

	public void update() {
		ball.moveBall();
		repaint();
	}
}



public class Ball extends JLabel {
	private static final long serialVersionUID = 1L;
	int x = 150;
	int y = 150;

	int xVelocity = 1;
	int yVelocity = 1;

	public void paintBall(Graphics g) {
		g.fillOval(x, y, 25, 25);
	}

	public void moveBall() {
		if (x >= (getWidth() - 50) || x <= 0) {
			xVelocity = -xVelocity;
		}
		if (y >= getHeight() - 50 || y <= 0)
			yVelocity = -yVelocity;
		x += xVelocity;
		y += yVelocity;
	}
}



public class BallEngine extends Thread {
	GamePanel gamepanel = new GamePanel();

	public BallEngine(GamePanel gamepanel) {
		this.gamepanel = gamepanel;
	}

	@Override
	public void run() {
		while (true) {
			try {
				gamepanel.update();

			} catch (Exception e) {
			}
		}
	}
}
#2

You didn’t post your Paddle class, so we can’t run this code.

You might consider posting an MCVE, a single file that we can easily copy-paste into our own IDEs to run.

But I have a few questions:

Why do you have a Ball instance in your GUI class that you don’t seem to do anything with?
Why do you create a GamePanel in your GUI class, and another GamePanel in your BallEngine class? You then throw away the GamePanel in the BallEngine class, so why bother creating it?
Why on earth does Ball extend JLabel?
Why do you have an empty catch block?
Why are you modifying variables (Ball x and y) from one Thread (GameEngine) while using them in another Thread (the EDT calling paintComponent)?

Since your Ball class extends JLabel, when you call getWidth() and getHeight() in your Ball class, you’re referring to the width and height of the JLabel itself. you probably want to refer to the width and height of the JPanel or the JFrame instead.