java - 线程 "AWT-EventQueue-0"java.lang.NullPointerException 中的异常？ java

Question

我是 java 的新手，需要帮助解决我面临的问题。这可能是一个愚蠢的错误，所以请原谅我。

    Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at javax.swing.ImageIcon.<init>(Unknown Source)
at Game.actionPerformed(Game.java:65)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$200(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

是我的错

    import javax.swing.*;
    import java.awt.*;
    import java.awt.event.*;
    import java.util.Timer;
    @SuppressWarnings("serial")
    public class Game extends JFrame implements ActionListener , KeyListener {

    static Dimension screenSize = new         Dimension(Toolkit.getDefaultToolkit().getScreenSize());
    Insets scnMax = Toolkit.getDefaultToolkit().getScreenInsets(getGraphicsConfiguration());
    int taskBarSize = scnMax.bottom;
    static JFrame startScreen = new JFrame("Start");
    static JFrame game = new JFrame("Begin!");
    static JLabel cow = new JLabel();
    static int Sky = 1;
    static JLabel sky = new JLabel();
    static int seconds = 1;
    static boolean isPressed = false;
public static void main(String[] args) {
    new Game();

}
public Game() {

    JPanel buttons = new JPanel();
    buttons.setLayout(null);
    startScreen.setSize(new Dimension(screenSize.width - getWidth(), screenSize.height - taskBarSize - getHeight()));
    startScreen.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    startScreen.setVisible(true);
    System.out.println(startScreen.getSize());
    //buttons 

    JButton Start = new JButton("Start");
    Start.addActionListener(this);
    Start.setSize((int) startScreen.getWidth()/7, (int) (startScreen.getHeight()/15.36));
    Start.setBounds((startScreen.getWidth()/2) - Start.getWidth()/2,((int)startScreen.getHeight()/2) - Start.getHeight(),Start.getWidth(),Start.getHeight());
    Start.setActionCommand("Start");

    buttons.add(Start);
    startScreen.add(buttons);
}
@Override
public void actionPerformed(ActionEvent evt) {
    Object cmd =  evt.getActionCommand();
    if(cmd == "Start") {
        startScreen.setVisible(false);
        ImageIcon Cow = new ImageIcon(getClass().getResource("/cow.png"));
        ImageIcon Grass = new   ImageIcon(getClass().getResource("/grass.png"));

        game.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        game.setSize(startScreen.getSize());
        game.setVisible(true);
        JPanel pan = new JPanel();
        pan.setBackground(Color.white);
        pan.setLayout(null);
        pan.setFocusable(true);
        game.add(pan);
        pan.addKeyListener(this);
        cow.setBounds( (startScreen.getWidth()/2)-105, (startScreen.getHeight()/2)-55, 210, 111);
        cow.setIcon(Cow);
        pan.add(cow);
        pan.setVisible(true);
        cow.setVisible(true);
        JLabel grass = new JLabel();
        System.out.println("grass");
        ImageIcon Sky1 = new ImageIcon(getClass().getResource("/Sky.png"));
        sky.setIcon(Sky1);
        grass.setIcon(Grass);
        grass.setBounds(0, ( startScreen.getHeight()-308), startScreen.getWidth(), 350);
        System.out.println("meow");
        pan.add(grass);
        sky.setBounds(1, 56, 1366, 364);
        pan.add(sky);
        System.out.println("google");
    }

}
@Override
public void keyPressed(KeyEvent e) {
    int cmd = e.getKeyCode();
    ImageIcon CowMoving = new ImageIcon(getClass().getResource("/cow moving.gif"));
    System.out.println(cmd);
    isPressed = true;
    if(cmd == 39){
        System.out.println("pressed");
        cow.setIcon(CowMoving);
    }
    else if(cmd == 37){

    }
    System.out.println("End");
    while(isPressed==true){         
        Timer wait = new Timer("Wait");
        try {
            wait.wait(1000);
        }
        catch(InterruptedException p){}
        int SKY = 1;
        SKY += 1;
        String SKYString = "/Sky" + String.valueOf(SKY) + ".png";
        ImageIcon SKy = new ImageIcon(getClass().getResource(SKYString));
        sky.setIcon(SKy);
        if(isPressed==false){
            wait.cancel();
            break;
        }
    }
}               



@Override
public void keyReleased(KeyEvent p) {
    ImageIcon Cow = new ImageIcon(getClass().getResource("/cow.png"));
    int cmd = p.getKeyCode();
    isPressed = false;
    if(cmd == 39){
        cow.setIcon(Cow);
    }
    else if(cmd == 37){
        cow.setIcon(Cow);
    }
}
@Override
public void keyTyped(KeyEvent c) {
    // TODO Auto-generated method stub      
    }
}

和我的代码。

我已经编写了大约两周的 Java 代码，并想到了一个愚蠢的练习项目。感谢您的帮助

Answer 1

看起来 getClass().getResource("/cow.png") 正在返回 null。为了使它不为空，cow.png 应该放在与 Game.class 相同的文件夹中。参见 related post

正如@camickr 在评论中指出的那样，您应该删除 / 就像 getClass().getResource("cow.png")