Bouncing shape - over-complicating it?

[Dodger]

Hi,

Following is the code I came up with, I get the feeling I over-complicated the program, please point me in the right direction, TIA.

import java.awt.*;
import javax.swing.*;

class BouncingDisplay extends JFrame
{
	public static void main(String[] arguments)
	{
		BouncingDisplay bd = new BouncingDisplay();
	}
	
	public BouncingDisplay()
	{
		super("Bouncing Display");
		setSize(400, 200);
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		
		BouncingPanel bp = new BouncingPanel();
		getContentPane().add(bp);
		
		setVisible(true);
	}
}

class BouncingPanel extends JPanel implements Runnable
{
	Thread runner;
	int x;
	int y;
	
	public BouncingPanel()
	{
		setSize(200, 200);
		Thread runner = new Thread(this);
		runner.start();
	}
	
	public void run()
	{
		char x_dir = '+';
		char y_dir = '+';
		 
		while(true)
		{	
			if(x_dir == '+')
			{
				if(x > getSize().width - 10)
				{
					x_dir = '-';
					x -= 4;
				} else {
					x += 4;
				}
			} else {
				if(x <= 0)
				{
					x_dir = '+';
					x += 4;
				} else {
					x -= 4;
				}
			}
			
			if(y_dir == '+')
			{
				if(y > getSize().height - 10)
				{
					y_dir = '-';
					y -= 4;
				} else {
					y += 4;
				}
			} else {
				if(y <= 0)
				{
					y_dir = '+';
					y += 4;
				} else {
					y -= 4;
				}
			}
			
			repaint();
			
			try {
				Thread.sleep(100);
			} catch (InterruptedException e) {
			}
		}
	}
	
	public void paintComponent(Graphics canvas)
	{
		Graphics2D canvas2D = (Graphics2D)canvas;
		
		canvas2D.clearRect(0, 0, getSize().width, getSize().height);
		canvas2D.setColor(Color.blue);
		canvas2D.fillRect(x, y, 10, 10);
	}
}

D.