Display.java

package aplicacion;
import java.awt.Canvas;
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.image.BufferStrategy;

import javax.swing.JFrame;
public class Display extends Canvas implements Runnable{
	private static final long serialVersionUID= -1;
	public static int  WIDTH=800, HEIGHT = 600;
	private boolean  running= false;
	public int FPS;
	private Thread  thread;
	public static void main(String[] args) {
		Display display = new Display();
		JFrame frame = new JFrame();
		frame.add(display);
		frame.pack();
		frame.setTitle("Space Invaders");
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setResizable(false);
		frame.setVisible(true);
		display.start();
	}

	public synchronized void start() {
		if (running)
			return;

		running = true;

		thread = new Thread(this);
		thread.start();
	}

	public synchronized void stop() {
		if (!running)
			return;

		running = false;

		try {
			thread.join();
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}

	public static GameScreen game;
	public Display() {
		this.setSize(WIDTH, HEIGHT);
		this.setFocusable(true);

		game = new GameScreen();
		game.init(this);
	}
	@Override
	public void run() {
		long timer = System.currentTimeMillis();
		long lastLoopTime = System.nanoTime();
		final int TARGET_FPS = 60;
		final long OPTIMAL_TIME = 1000000000 / TARGET_FPS;
		int frames = 0;

		this.createBufferStrategy(3);
		BufferStrategy bs = this.getBufferStrategy();
		while (running) {
			long now = System.nanoTime();
			long updateLength = now - lastLoopTime;
			lastLoopTime = now;
			double delta = updateLength / ((double) OPTIMAL_TIME);			
			draw(bs);
			update(delta);
		}
	}

	public void draw(BufferStrategy bs) {
		do {
			do {
				Graphics2D g = (Graphics2D) bs.getDrawGraphics();
				g.setColor(Color.BLACK);
				g.fillRect(0, 0, WIDTH + 50, HEIGHT + 50);
				
				game.draw(g);

				g.dispose();
			} while (bs.contentsRestored());
			bs.show();
		} while (bs.contentsLost());
	}

	public void update(double delta) {
		game.update(delta);
	}

}