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我對java比較陌生，需要幫助解決一個面臨的問題。這可能是一個愚蠢的錯誤，所以請原諒我。線程「AWT-EventQueue-0」中的異常java.lang.NullPointerException？ Java
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)
是我的錯誤
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
}
}
和我的代碼。
我一直在編寫java約兩週，並認爲一個愚蠢的項目的實踐。 感謝您的幫助
請勿使用靜態變量。不要使用空佈局。使用適當的變量名稱。變量名稱不應以大寫字符開頭。 「開始」應該是「開始」。不要使用「==」來比較字符串，請使用equals（）方法。我想這個問題是文件路徑中的前導「/」。擺脫它。 – camickr
請看看這個[回覆]（http://stackoverflow.com/a/9866659/1057230），如果你在沒有IDE的情況下做所有事情，請訪問它的最後一個鏈接。 –