沒有按鍵時球停止移動嗎？

Question

這裏是我的代碼：

public class Main extends Applet implements Runnable, KeyListener, 
    java.awt.event.MouseListener { 
int x_pos = 300; 
int y_pos = 200; 
int radius = 20; 
int appletsize_x = 600; 
int appletsize_y = 400; 
double x_speed = 0; 
double y_speed = 0; 

private Image dbImage; 
private Graphics dbg; 

public void init() { 
    this.setSize(600, 400); 

} 

public void start() { 

    this.addKeyListener(this); 
    this.addMouseListener(this); 
    Thread th = new Thread(this); 
    th.start(); 
} 

public void stop() { 

} 

public void destroy() { 

} 

public void run() { 

    // lower ThreadPriority 
    this.requestFocusInWindow(); 
    Thread.currentThread().setPriority(Thread.MIN_PRIORITY); 

    while (true) { 

     repaint(); 
     x_pos += x_speed; 
     y_pos += y_speed; 

     // Hitting (right) 
     if (x_pos > this.getSize().width - radius) { 

      //x_speed = -x_speed; 
      x_speed = 0; 

     } 
     // Hitting (left) 
     if (x_pos < 0 + radius) { 

      //x_speed = -x_speed; 
      x_speed = 0; 

     } 
     // Hitting top 
     if (y_pos < 0 + radius) { 


      //y_speed = -y_speed; 
      y_speed = 0; 

     } 

     // Hitting bottom 
     if (y_pos > this.getSize().height - radius) { 

      //y_speed = -y_speed; 
      y_speed = 0; 

     } 

     try { 
      // Stop thread for 1 milliseconds 
      Thread.sleep(20); 
     } catch (InterruptedException ex) { 
      // do nothing 
     } 

     // set ThreadPriority to maximum value 
     Thread.currentThread().setPriority(Thread.MAX_PRIORITY); 

    } 
} 

public void paint(Graphics g) { 
    // set colour 
    g.setColor(Color.red); 

    // paint a filled coloured circle 
    g.fillOval(x_pos - radius, y_pos - radius, 2 * radius, 2 * radius); 
} 

public void update(Graphics g) { 

    if (dbImage == null) { 
     dbImage = createImage(this.getSize().width, this.getSize().height); 
     dbg = dbImage.getGraphics(); 
    } 

    dbg.setColor(getBackground()); 
    dbg.fillRect(0, 0, this.getSize().width, this.getSize().height); 

    dbg.setColor(getForeground()); 
    paint(dbg); 

    g.drawImage(dbImage, 0, 0, this); 
} 

@Override 
public void keyPressed(KeyEvent e) { 
    if (e.getKeyCode() == KeyEvent.VK_LEFT) { 
     if (x_speed > 0) { 
      x_speed = +x_speed; 
      y_speed = 0; 
     } 
     if (x_speed == 0) { 
      x_speed = -4; 
      y_speed = 0; 
     } 
     if (x_speed < 0) { 
      x_speed = +x_speed; 
      y_speed = 0; 
     } 
    } 
    if (e.getKeyCode() == KeyEvent.VK_RIGHT) { 
     if (x_speed < 0) { 
      x_speed = -x_speed; 
      y_speed = 0; 

      if (x_speed > 0) { 
       x_speed = -x_speed; 
       y_speed = 0; 
      } 
     } 
     if (x_speed == 0) { 
      x_speed = 4; 
      y_speed = 0; 
     } 

    } 
    if (e.getKeyCode() == KeyEvent.VK_UP) { 
     if (y_speed > 0) { 
      y_speed = -y_speed; 
      x_speed = 0; 
     } 
     if (y_speed < 0) { 
      y_speed = +y_speed; 
      x_speed = 0; 
     } 
     if (y_speed == 0) { 
      y_speed = -4; 
      x_speed = 0; 
     } 
    } 
    if (e.getKeyCode() == KeyEvent.VK_DOWN) { 
     if (y_speed > 0) { 
      y_speed = +y_speed; 
      x_speed = 0; 
     } 
     if (y_speed < 0) { 
      y_speed = -y_speed; 
      x_speed = 0; 
     } 
     if (y_speed == 0) { 
      y_speed = +4; 
     } 
     x_speed = 0; 
    } 
} 

@Override 
public void keyReleased(KeyEvent e) { 
    // TODO Auto-generated method stub 

} 

@Override 
public void keyTyped(KeyEvent e) { 
    // TODO Auto-generated method stub 

} 

@Override 
public void mouseClicked(MouseEvent e) { 
    System.out.println("HIT!"); 
    // TODO Auto-generated method stub 

} 

@Override 
public void mouseEntered(MouseEvent e) { 
    // TODO Auto-generated method stub 

} 

@Override 
public void mouseExited(MouseEvent e) { 
    // TODO Auto-generated method stub 

} 

@Override 
public void mousePressed(MouseEvent e) { 
    // TODO Auto-generated method stub 

} 

@Override 
public void mouseReleased(MouseEvent e) { 
    // TODO Auto-generated method stub 

} 
     } 

我將如何使球停止沒有按任何按鍵時移動？

Answer 1

在你的keyReleased方法下，你應該可以做你的keyPressed方法的反面。也就是說，如果按下右箭頭鍵，則向x_speed中加1，當您釋放它時，從x_speed中減1，對其他鍵使用類似的邏輯。

Answer 2

你可以在keyReleased上使x_speed和y_speed等於0嗎？