"AWT-EventQueue-0" 图形 jpanel

Question

我是 Java 的新手，遇到了 "AWT-EventQueue-0" 错误。我尝试了很多搜索，但仍然无法修复我的代码。

我正在尝试用数字制作 Hangman 游戏，程序会创建一个 1 到 100 之间的随机数。然后程序将创建一个包含 100 个按钮的按钮网格。在你猜了 10 次之后，程序会显示一个弹出框，询问你是否想玩另一个游戏。如果你赢了，程序会发出哔哔声，弹出框会出现。

这是我的 GameFrame class，我在其中创建根面板和按钮网格：

...
public int wrongGuess = 5;

public GameFrame() {
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setSize(1000, 500);
        rootPanel.setLayout(new BoxLayout(rootPanel, BoxLayout.X_AXIS));
        rootPanel.add(getButtonGrid(), BorderLayout.CENTER);
        rootPanel.add(gp, BorderLayout.CENTER);
        add(rootPanel);
        setFocusable(true);
        setCentered(true);
        setVisible(true);
}

private Container getButtonGrid() {
    JPanel buttonsGrid = new JPanel(new GridLayout(10,10,0,0));
    Dimension d = new Dimension(0,20);
    for (int i = 1; i < buttons.length; i++) {
        buttons[i] = new JButton(String.valueOf(i));
        buttons[i].setPreferredSize(d);
        buttons[i].addActionListener(this);
        buttonsGrid.add(buttons[i]);
    }
    return buttonsGrid;
}

@Override public void actionPerformed(ActionEvent ae) {
    boolean win = false;
    wrongGuess = wrongGuess + 1;
    setWrongGuess(wrongGuess);
    int buttonNumber = Integer.valueOf(((JButton) ae.getSource()).getActionCommand());
    if (buttonNumber == ge.getGuessingNumber()) {
        win = true;
        buttons[buttonNumber].setBackground(new Color(60,179,113));
        buttons[buttonNumber].setOpaque(true);
        Toolkit.getDefaultToolkit().beep();
        ge.start();
    } else {
        if (buttonNumber > ge.getGuessingNumber()) {
            buttons[buttonNumber].setBackground(new Color(220,20,60));
            buttons[buttonNumber].setOpaque(true);
        }
        if (buttonNumber < ge.getGuessingNumber()) {
            buttons[buttonNumber].setBackground(new Color(255,255,102));
            buttons[buttonNumber].setOpaque(true);
        }
    }
    if (wrongGuess == 10) {
        win = true;
        ge.start();
        setWrongGuess(0);
    }
    if (win == true) {
        for (int i = 1; i < buttons.length; i++) {
            buttons[i].setBackground(null);
        }
    }
}
...

每当用户猜错时，我想显示一个"Hangman part"（例如手臂，腿...等）。

这是我的游戏面板class：

GameFrame gf;

public GamePanel() {
    this.setSize(500, 500);
    this.setVisible(true);
    this.setFocusable(true);
}

public void paint(Graphics comp) {
    super.paintComponent(comp);
    int wrongGuess = gf.wrongGuess;

    if (wrongGuess == 5) {
        comp.drawOval(162, 150, 50, 50);
        comp.drawLine(188, 200, 188, 275);
        comp.drawLine(148, 235, 188, 215);
        comp.drawLine(188, 215, 228, 235);
        comp.drawLine(188, 275, 228, 335);
        comp.drawLine(148, 335, 188, 275);
    }
    repaint();
}

我假设我错误地声明了 "wrongGuess" 但我不知道我做错了什么。谁能帮我找到解决此错误的正确方法？

我的错误：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at micro.project.GamePanel.paint(GamePanel.java:21)
at javax.swing.JComponent.paintChildren(JComponent.java:889)
at javax.swing.JComponent.paint(JComponent.java:1065)
at javax.swing.JComponent.paintChildren(JComponent.java:889)
at javax.swing.JComponent.paint(JComponent.java:1065)
at javax.swing.JComponent.paintChildren(JComponent.java:889)
at javax.swing.JComponent.paint(JComponent.java:1065)
at javax.swing.JLayeredPane.paint(JLayeredPane.java:586)
at javax.swing.JComponent.paintChildren(JComponent.java:889)
at javax.swing.JComponent.paintToOffscreen(JComponent.java:5217)
at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1579)
at javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1502)
at javax.swing.RepaintManager.paint(RepaintManager.java:1272)
at javax.swing.JComponent.paint(JComponent.java:1042)
at java.awt.GraphicsCallback$PaintCallback.run(GraphicsCallback.java:39)
at sun.awt.SunGraphicsCallback.runOneComponent(SunGraphicsCallback.java:79)
at sun.awt.SunGraphicsCallback.runComponents(SunGraphicsCallback.java:116)
at java.awt.Container.paint(Container.java:1975)
at java.awt.Window.paint(Window.java:3904)
at javax.swing.RepaintManager.run(RepaintManager.java:842)
at javax.swing.RepaintManager.run(RepaintManager.java:814)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:80)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:814)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:789)
at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:738)
at javax.swing.RepaintManager.access00(RepaintManager.java:64)
at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1732)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756)
at java.awt.EventQueue.access0(EventQueue.java:97)
at java.awt.EventQueue.run(EventQueue.java:709)
at java.awt.EventQueue.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:80)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:726)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

PS: 抱歉我的英语不好

Answer 1

这是一个典型的空指针异常，任何时候你声明一个像

这样的引用

GameFrame gf;

然后像 gf.wrongGuess() 一样引用它；没有实例化

这样的对象

gf = new GameFrame();

gf 不会指向任何对象，它只是对任何对象的引用，所以它会抛出 NPE

Answer 2

对GameFrame的引用是GamePanel中的null，您需要将GameFrame的引用传递给GamePanel...

GameFrame gf;

public GamePanel(GameFrame gf) {
    this.gf = gf;
    // Pointless as the layout manager will take care of it
    //this.setSize(500, 500);
    // Pointless as Swing components are visible by default
    //this.setVisible(true);
    this.setFocusable(true);
}

@Overrride
protected void paintComponent(Graphics comp) {
    super.paintComponent(comp);
    int wrongGuess = gf.wrongGuess;

    if (wrongGuess == 5) {
        comp.drawOval(162, 150, 50, 50);
        comp.drawLine(188, 200, 188, 275);
        comp.drawLine(148, 235, 188, 215);
        comp.drawLine(188, 215, 228, 235);
        comp.drawLine(188, 275, 228, 335);
        comp.drawLine(148, 335, 188, 275);
    }
    // Don't do this here, this will cause no end of issues
    //repaint();
}

此外，您重写了 paint 但调用了 super.paintComponent，这会破坏整个绘制链 - 除非您真的知道自己在做什么，否则不要这样做。相反，如所示，只需覆盖 paintComponent

"AWT-EventQueue-0" 图形 jpanel

"AWT-EventQueue-0" graphics jpanel

java

int

jpanel

jframe

jbutton