Java flikkerend beeld

package eu.inmensia.learn;

import java.awt.Canvas;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.image.BufferStrategy;

import javax.swing.JFrame;

public class Client extends Canvas implements Runnable {
    private static final long serialVersionUID = 1L;

    public static final int WIDTH = 300;
    public static final int HEIGHT = WIDTH / 16 * 9;
    public static final byte SCALE = 3;

    private Thread thread;
    private JFrame frame = new JFrame();
    private boolean running = false;

    public Client() {
        Dimension size = new Dimension(WIDTH * SCALE, HEIGHT * SCALE);
        setPreferredSize(size);
    }

    public synchronized void start() {
        running = true;
        thread = new Thread(this, "display");
        thread.start(); // starts the thread
    }

    public synchronized void stop() {
        running = false;
        try {
            thread.join(); // ends the thread
        } catch(InterruptedException e){ e.printStackTrace(); }
    }

    public void run() {
        while(running){
            tick();
            render();
        }
    }

    public void tick() {

    }

    public void render() {
        BufferStrategy bs = getBufferStrategy();
        if(bs == null){
            createBufferStrategy(3);
            return;
        }

        Graphics g = bs.getDrawGraphics();
        {
            // background
            g.setColor(Color.BLACK);
            g.drawRect(0, 0, getWidth(), getHeight());
        }
        g.dispose();
        bs.show();
    }

    public static void main(String[] args) {
        Client client = new Client();
        client.frame.setResizable(false);
        client.frame.setTitle("Learning");
        client.frame.add(client);
        client.frame.pack();
        client.frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        client.frame.setLocationRelativeTo(null);
        client.frame.setVisible(true);

        client.start();
    }
}