我正在尝试将 CardLayout 中的卡片从我的游戏 JPanel 切换到我的 gameOver JPanel。游戏没有切换屏幕，而是崩溃了。感谢您提前提出的任何建议。
我的游戏代码：
public class Game extends JPanel implements KeyListener {
private Player player;
private Stage stage;
private Stage stageLeft;
private Stage stageRight;
private EnemyManager manager;
private Window windowInstance;
private boolean isGameOver = false;
private boolean restart = false;
public Game() {
setSize(800,600);
setPreferredSize(new Dimension(800,600));
setFocusable(true);
setBackground(Color.WHITE);
requestFocus();
addKeyListener(this);
stage = new Stage(0, 540, 800, 100);
stageLeft = new Stage(-1, 0, 1, 600);
stageRight = new Stage(800, 0, 1, 600);
player = new Player(this, 400, 400);
manager = new EnemyManager(this, 10);
}
@Override
public void update(Graphics g) {
paint(g);
}
public void paint(Graphics g) {
g.setColor(Color.WHITE);
g.fillRect(0,0,getWidth(),getHeight());
stage.draw(g);
stageLeft.draw(g);
stageRight.draw(g);
if(!isGameOver || restart) {
player.draw(g);
manager.draw(g);
} else {
g.setColor(Color.BLACK);
g.fillRect(0, 0, getWidth(), getHeight());
g.setColor(Color.WHITE);
g.setFont(new Font("Century Gothic", Font.BOLD, 24));
g.drawString("Game Over!", 330, 300);
//TODO: FIX CRASH ERROR
if(!windowInstance.getGameOver()) {
windowInstance.setGameOver(true);
}
}
g.dispose();
repaint();
}
@Override
public void keyPressed(KeyEvent e) {
int c = e.getKeyCode();
if(c == KeyEvent.VK_W) {
}
if(c == KeyEvent.VK_A) {
player.setxDir(-1);
}
if(c == KeyEvent.VK_S) {
}
if(c == KeyEvent.VK_D) {
player.setxDir(1);
}
}
public void setGameOver(boolean flag) {
isGameOver = flag;
}
@Override
public void keyReleased(KeyEvent e) {
player.setxDir(0);
player.setyDir(0);
}
@Override
public void keyTyped(KeyEvent e) {
}
public Stage getStage() {
return stage;
}
public Stage getStageLeft() { return stageLeft; }
public Stage getStageRight() { return stageRight; }
public EnemyManager getEnemyManager() {
return manager;
}
}
我的窗口代码（错误似乎是由将 CardLayout 切换到 gameOver JPanel 引起的）：
public class Window {
JFrame frame = new JFrame("Cube Fall");
JPanel panelContainer = new JPanel();
JPanel startMenu = new JPanel();
Game game = new Game();
JPanel gameOver = new JPanel();
CardLayout cardLayout = new CardLayout();
// Constructor
public Window() {
// Layout Stuff
panelContainer.setLayout(cardLayout);
panelContainer.add(startMenu, "0");
panelContainer.add(game, "1");
panelContainer.add(gameOver, "2");
cardLayout.show(panelContainer, "0");
// Setup startMenu
JButton startButton = new JButton("Start");
startMenu.add(startButton);
startMenu.setBackground(Color.BLACK);
startButton.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent actionEvent) {
cardLayout.show(panelContainer, "1");
game.grabFocus();
}
});
// Setup gameOver
JButton restartButton = new JButton("Restart");
gameOver.add(restartButton);
gameOver.setBackground(Color.BLACK);
restartButton.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent actionEvent) {
cardLayout.show(panelContainer, "1");
game.grabFocus();
}
});
frame.add(panelContainer);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setVisible(true);
frame.setResizable(false);
frame.requestFocus();
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
new Window();
}
});
/*
Game game = new Game();
JFrame frame = new JFrame();
frame.setTitle("Java Game");
frame.add(game);
frame.pack();
frame.setPreferredSize(new Dimension(800,600));
frame.setResizable(false);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// Center window
frame.setLocationRelativeTo(null);
frame.setVisible(true);*/
}
public JFrame getFrame() {
return frame;
}
private boolean trueOrFalse = false;
public void setGameOver(boolean tof) {
if(tof) {
JButton restartButton = new JButton("Restart");
restartButton.setLocation(300,300);
game.add(restartButton);
restartButton.setVisible(true);
game.revalidate();
//cardLayout.show(panelContainer, "2");
trueOrFalse = true;
}
}
public boolean getGameOver() {
return trueOrFalse;
}
}
我得到的错误如下：
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at Game.paint(Game.java:59)
at javax.swing.JComponent._paintImmediately(JComponent.java:5106)
at javax.swing.JComponent.paintImmediately(JComponent.java:4890)
at javax.swing.RepaintManager$3.run(RepaintManager.java:814)
at javax.swing.RepaintManager$3.run(RepaintManager.java:802)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:86)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:802)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:745)
at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:725)
at javax.swing.RepaintManager.access$1000(RepaintManager.java:46)
at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1680)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:715)
at java.awt.EventQueue.access$400(EventQueue.java:82)
at java.awt.EventQueue$2.run(EventQueue.java:676)
at java.awt.EventQueue$2.run(EventQueue.java:674)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:86)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:685)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)