问Java Swing移动卡顿

EN

package movementstutter;

import javax.swing.JFrame;

public class MovementStutter {

public static void main(String[] args) {
    JFrame win = new JFrame("Stutter Demo");
    win.getContentPane().add(new GamePanel());
    win.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    win.setResizable(false);
    win.pack();
    win.setVisible(true);
}

}

package movementstutter;

import java.awt.Dimension;
import java.awt.Graphics;
import javax.swing.JPanel;

public class GamePanel extends JPanel implements Runnable {

private boolean running;
private Thread thread;
private double x;
private double y;
private double movementFactor;

public GamePanel() {
    setPreferredSize(new Dimension(640, 480));
    setFocusable(true);
    grabFocus();
    movementFactor = 1;
    running = true;
}

@Override
public void addNotify() {
    super.addNotify();
    if (thread == null) {
        thread = new Thread(this);
        thread.start();
    }
}

@Override
public void run() {
    long time = System.currentTimeMillis();
    while (running) {
        update();
        repaint();
        long sleep = 16 - (System.currentTimeMillis() - time);
        time += 16;
        if (sleep < 0) {
            sleep = 16;
        }
        try {
            Thread.sleep(sleep);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

private void update() {
    if (x < 0) {
        movementFactor = 1;
    } else if (x > 608) {
        movementFactor = -1;
    }
    x += movementFactor * 200 * 0.016;
}

@Override
public void paintComponent(Graphics g) {
    super.paintComponent(g);
    g.fillRect((int) x, (int) y, 32, 32);
}

}