Bouncing ball Slick2D demo

DemoSprite.java

package com.musante.demo;

import org.newdawn.slick.AppGameContainer;
import org.newdawn.slick.BasicGame;
import org.newdawn.slick.GameContainer;
import org.newdawn.slick.Graphics;
import org.newdawn.slick.Image;
import org.newdawn.slick.SlickException;

/**
 * Slick bouncing-sprite demo
 * @author maxx
 * Apr 13, 2013
 * Copyright (c) Massimo Musante 2013
 */
public class DemoSprite extends BasicGame
{
	private int x = 100;
	private int y = 100;
	private int dx = 1;
	private int dy = 1;
	private Image img = null;
	
	public DemoSprite()
	{
		super("Demo Sprite");
	}

	/*
	 * (non-Javadoc)
	 * @see org.newdawn.slick.Game#render(org.newdawn.slick.GameContainer, org.newdawn.slick.Graphics)
	 */
	@Override
	public void render(GameContainer gc, Graphics g) throws SlickException
	{
		img.draw(x, y);		
	}

	/*HelloSprite
	 * (non-Javadoc)
	 * @see org.newdawn.slick.BasicGame#init(org.newdawn.slick.GameContainer)
	 */
	@Override
	public void init(GameContainer gc) throws SlickException
	{
		img = new Image("res/ball.png");
	}

	/*
	 * (non-Javadoc)
	 * @see org.newdawn.slick.BasicGame#update(org.newdawn.slick.GameContainer, int)
	 */
	@Override
	public void update(GameContainer gc, int delta) throws SlickException
	{
		if(x>gc.getWidth()-img.getWidth()) dx = -1;
		if(x<0) dx = 1;
		if(y>gc.getHeight()-img.getHeight()) dy = -1;
		if(y<0) dy = 1;		
		x = x+dx;
		y = y+dy; 		
	}
	
	/**
	 * Start the demo, no parameters
	 * @param args
	 * @throws SlickException
	 */
	public static void main(String[] args) throws SlickException
	{
		AppGameContainer app = new AppGameContainer(new DemoSprite());
		app.setDisplayMode(300, 200, false);
		app.start();
	}	

}