使用KeyListener的Pong控件

您有一个重点问题。您正在向JPanel添加KeyListener：但是JPanel永远不会具有焦点，因此KeyListener将无法工作：

public class Pong extends JPanel{    //...    public Pong(Color backcolor, int Width, int Height)    {        // ...        timer =  new javax.swing.Timer(5, new MoveListener());        addKeyListener(new KeyWatcher());

但是JPanel永远不会获得焦点，并且KeyListeners仅在被侦听的组件具有焦点时才起作用。

更好的解决方案不是中继KeyListener，而是使用Swing Timer和Key
Bindings。请参阅[此链接](http://codingdict.com/questions/2408以获取此示例。

编辑 ：或者甚至更好的链接-JavaKeyListener不注册箭头键。

编辑2
也许更好的解决方案是使用按键绑定，但是使用它们在按键或释放按键时设置类的字段，然后使用Swing Timer作为游戏循环来轮询这些字段。

例如，这不会显示动画（由您决定），但是表明此技术将允许对同时按下的键做出响应：

import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import java.awt.event.KeyEvent;import java.util.EnumMap;import javax.swing.*;public class NewArrowTest extends JPanel {   private static final String PRESSED = "pressed";   private static final String RELEASED = "released";   private static final int TIMER_DELAY = 20;   private EnumMap<Key, Boolean> keyMap = new EnumMap<NewArrowTest.Key, Boolean>(Key.class);   public NewArrowTest() {      keyMap.put(Key.W, false);      keyMap.put(Key.S, false);      keyMap.put(Key.UP, false);      keyMap.put(Key.DOWN, false);      // set up key binding      ActionMap actionMap = getActionMap();      int condition = JComponent.WHEN_IN_FOCUSED_WINDOW;      InputMap inputMap = getInputMap(condition);      for (Key key : Key.values()) {         KeyStroke pressedKeyStroke = KeyStroke.getKeyStroke(key.getKeyCode(), 0, false);         KeyStroke releasedKeyStroke = KeyStroke.getKeyStroke(key.getKeyCode(), 0, true);         inputMap.put(pressedKeyStroke, key.getText() + PRESSED);         inputMap.put(releasedKeyStroke, key.getText() + RELEASED);         actionMap.put(key.getText() + PRESSED, new MyArrowBinding(key, false));         actionMap.put(key.getText() + RELEASED, new MyArrowBinding(key, true));      }      // start polling timer or game loop      new Timer(TIMER_DELAY, new TimerListener()).start();   }   private static void createAndShowGui() {      NewArrowTest mainPanel = new NewArrowTest();      Jframe frame = new Jframe("NewArrowTest");      frame.setDefaultCloseOperation(Jframe.EXIT_ON_CLOSE);      frame.getContentPane().add(mainPanel);      frame.pack();      frame.setLocationByPlatform(true);      frame.setVisible(true);   }   public static void main(String[] args) {      SwingUtilities.invokeLater(new Runnable() {         public void run() { createAndShowGui();         }      });   }   private class TimerListener implements ActionListener {      public void actionPerformed(java.awt.event.ActionEvent e) {         for (Key key : keyMap.keySet()) { System.out.printf("%6s %b%n", key, keyMap.get(key)); // here we'd move things based on which key is true         }         System.out.println();      };   }   private class MyArrowBinding extends AbstractAction {      private Key key;      private boolean released;      public MyArrowBinding(Key key, boolean released) {         this.key = key;         this.released = released;      }      @Override      public void actionPerformed(ActionEvent aEvt) {         keyMap.put(key, !released);      }   }   enum Direction {      UP("Up"), DOWN("Down"), NEUTRAL("Neutral");      private String text;      private Direction(String text) {         this.text = text;      }      public String getText() {         return text;      }   }   enum Key {      W("W", Direction.UP, KeyEvent.VK_W), S("S", Direction.DOWN, KeyEvent.VK_S),       UP("Up", Direction.UP, KeyEvent.VK_UP), DOWN("Down", Direction.DOWN, KeyEvent.VK_DOWN);      private String text;      private Direction direction;      private int keyCode;      private Key(String text, Direction direction, int keyCode) {         this.text = text;         this.direction = direction;         this.keyCode = keyCode;      }      public String getText() {         return text;      }      public Direction getDirection() {         return direction;      }      public int getKeyCode() {         return keyCode;      }   }}