在围绕屏幕移动球的情况下，如何正确处理JComponent的按键和重绘？

似乎您从未初始化过

actionPress

actionPress = new ActionPress();

即，您的构造函数将如下所示

public BallComponent(){    super();    super.setFocusable(true);    InputMap imap1 = this.getInputMap(JComponent.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT);    imap1.put(KeyStroke.getKeyStroke("ctrl Y"), "keyUp1");    InputMap imap2 = this.getInputMap(JComponent.WHEN_FOCUSED);    imap1.put(KeyStroke.getKeyStroke("ctrl Y"), "keyUp2");    InputMap imap3 = this.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW);       imap1.put(KeyStroke.getKeyStroke("ctrl Y"), "keyUp3");    actionPress = new ActionPress();    ActionMap amap = this.getActionMap();    amap.put("keyUp1", actionPress);    amap.put("keyUp2", actionPress);        amap.put("keyUp3", actionPress);}