import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class Game extends JPanel implements KeyListener {

    boolean[] keys = new boolean[1000];
    double x = 100;
    double y = 100;
    JFrame frame;

    public Game() {
        this.setBackground(Color.BLACK);
        frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.addKeyListener(this);
        frame.add(this);
        frame.setSize(640, 480);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);

        loop();
    }

    private void loop() {
        while (true) {
            long t0 = System.currentTimeMillis();
            repaint();
            logic();
            long duration = System.currentTimeMillis() - t0;

            if (duration < 16) {
                try {
                    Thread.sleep(16 - duration);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    private void logic() {
        double speed = 3.0;
        if (keys[KeyEvent.VK_UP]) {
            y -= speed;
        }
        if (keys[KeyEvent.VK_DOWN]) {
            y += speed;
        }
        if (keys[KeyEvent.VK_LEFT]) {
            x -= speed;
        }
        if (keys[KeyEvent.VK_RIGHT]) {
            x += speed;
        }
        if (keys[KeyEvent.VK_ESCAPE]) {
            System.exit(0);
        }
    }

    @Override
    public void paint(Graphics g) {
        super.paint(g);
        g.setColor(Color.WHITE);
        g.fillRect((int) x, (int) y, 30, 30);
    }

    public static void main(String[] args) {
        new Game();
    }

    @Override
    public void keyPressed(KeyEvent e) {
        keys[e.getKeyCode()] = true;
    }

    @Override
    public void keyReleased(KeyEvent e) {
        keys[e.getKeyCode()] = false;
    }

    @Override
    public void keyTyped(KeyEvent e) {
    }
}