键绑定将随机停止工作

Question

我正在尝试制作一款可以四处走动的游戏，而我已经为此发布了一个问题，here。然后有人告诉我tru KeyBindings，我设法创建了这个小型Keyboard类，以获取有关键的常规信息，但我仍然遇到与以前相同的问题：它仅在几秒钟内有效，然后才停止工作，而不会引发任何异常。

代码如下：

public class Keyboard {
private static final HashMap<Integer, Boolean> keys = new HashMap<Integer, Boolean>();
private static final int[] alphabet = new int[] {KeyEvent.VK_W, KeyEvent.VK_A, KeyEvent.VK_S, KeyEvent.VK_D, KeyEvent.VK_P};

@SuppressWarnings("serial")
public static void start(JPanel component) {
for(int c : alphabet) {
        keys.put(KeyStroke.getKeyStroke(c, 0, false).getKeyCode(), false);
        component.getInputMap(JPanel.WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke(c, 0, false), c);
        component.getActionMap().put(c, new AbstractAction() {
            @Override
            public void actionPerformed(ActionEvent e) {
                System.out.println("Pressed:" + c);
                keys.put(c, true);
            }
        });
        component.getInputMap(JPanel.WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke(c, 0, true), -c);
        component.getActionMap().put(-c, new AbstractAction() {
            @Override
            public void actionPerformed(ActionEvent e) {
                System.out.println("Released:" + c);
                keys.put(c, false);
            }
        });
    }
}

public static boolean isPressed(int key) {
    return keys.get(key);
}

}

感谢您的帮助！