Question

我想用键盘来唤起电脑的某些反应。所以我写了一个KeyEventDispatcher，但是我得到了一个NullPointerException。我无法说出异常发生在哪一行，因为编译器在任何情况下都指向同一行，无论是否存在代码或不存在代码。但是这个方法似乎被调用了，因为它打印出“test”。

以下是相关代码：

import java.util.*;
import java.awt.event.KeyEvent;
import java.awt.event.*;
import javax.swing.*;
import java.awt.KeyboardFocusManager;
import java.awt.KeyEventDispatcher;

public class Game extends JFrame
{
  private JFrame frame;

  public Game()
  {
    frame = new JFrame();
    KeyEventDispatcher keyEventDispatcher = new InputKeyListener();
        KeyboardFocusManager.getCurrentKeyboardFocusManager().addKeyEventDispatcher(keyEventDispatcher);
    frame.setFocusable(true);
    setFocusTraversalKeysEnabled(false);
    setVisible(true);
}

private class InputKeyListener implements KeyEventDispatcher
{   
    private KeyEvent e;

    @Override 
    public boolean dispatchKeyEvent(KeyEvent e) {
        System.out.println(e);
        if (e.getKeyCode() == KeyEvent.VK_RIGHT) {
            System.out.println("test");                    
        }

        if (e.getKeyCode() == KeyEvent.VK_LEFT) {
            //do something                    
        }
        if (e.getKeyCode() == KeyEvent.VK_DOWN){

        }
        if (e.getKeyCode() == KeyEvent.VK_R){

        }

        return false;
    }
}

这是堆栈跟踪：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at Spiel$InputKeyListener.dispatchKeyEvent(Spiel.java:43)
at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:1020)
at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:899)
at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:727)
at java.awt.Component.dispatchEventImpl(Component.java:4731)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:729)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:688)
at java.awt.EventQueue$3.run(EventQueue.java:686)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:702)
at java.awt.EventQueue$4.run(EventQueue.java:700)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:699)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

编辑：解决 - 问题不是代码而是BlueJ，我被老师强迫使用。虽然我经常重新编译，但我不知道为什么会执行旧代码。我不得不重新启动BlueJ以使其执行新代码。但感谢大家帮助我:)。

KeyEventDispatcher不起作用

0 个答案: