"AWT-EventQueue-0“图形jpanel

Question

我是Java的新手，遇到了"AWT-EventQueue-0“错误。我试着搜索了很多，但我仍然不能修复我的代码。

我正在尝试用数字做一个Hangman游戏，程序会创建一个介于1和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。你有10个猜测之后，程序将显示一个弹出框，并询问你是否想玩另一个游戏。如果你赢了，程序会发出蜂鸣声，弹出框也会出现。

下面是我的GameFrame类，我在其中创建了根面板和按钮网格：

...
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);
        }
    }
}
...

每次当用户有一个错误的猜测时，我想要显示一个"Hangman part“(例如：arm，leg...etc)。

下面是我的GamePanel类：

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。有没有人能帮我找到解决这个错误的正确方法？

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$4.run(RepaintManager.java:842)
at javax.swing.RepaintManager$4.run(RepaintManager.java:814)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$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.access$1200(RepaintManager.java:64)
at javax.swing.RepaintManager$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.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.awt.EventQueue$3.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$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)

附言:对不起，我的英语不好。

Answer 1

对GameFrame的引用是GamePanel中的null，相反，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，您正在重写paint但调用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，正如所演示的，只需覆盖paintComponent

Answer 2

这是一个典型的空指针异常，任何时候你声明一个引用，比如

GameFrame gf; 

然后像gf.wrongGuess()一样引用它；而不需要像这样实例化一个对象

gf = new GameFrame();

gf不会指向任何对象，它只是对nothing的引用，所以它抛出了一个NPE