我是编码的新手，我正在尝试制作基于文本，基于决策（因此称为1A变量和1B变量）的游戏。当我单击向西的JButton来唤起动作侦听器时，该程序将取消并显示此NullPointerException错误。
我已经尝试使用Eclipse调试器，但是当我这样做时，会弹出一个窗口，提示“ JDI线程评估遇到问题”。关于如何解决此问题有任何想法吗？
import java.awt.Color;
import java.awt.Container;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextArea;
public class The_Room {
JFrame window;
Container container;
JPanel titleNamePanel;
JPanel mainPanel;
JPanel textPanel1A;
JPanel go_northButtonPanel;
JPanel westButtonPanel;
JPanel textPanel2A;
JPanel lift_paintingButtonPanel;
JPanel go_west_insteadButtonPanel;
JPanel lift_mattressButtonPanel;
JPanel go_north_insteadButtonPanel;
JButton startButton;
JButton go_north;
JButton west;
JButton lift_painting;
JButton go_west_instead;
JButton lift_mattress;
JButton go_north_instead;
JTextArea TextArea1A; //A JLabel that allows multiple lines of text
JTextArea TextArea2A;
JTextArea TextArea2B;
JLabel titleNameLabel;
TitleScreenHandler handler = new TitleScreenHandler();
Screen1AHandler handler1A = new Screen1AHandler();
Screen1BHandler handler1B = new Screen1BHandler();
public static void main(String[] args) {
new The_Room();
}
public The_Room() {
window = new JFrame();
window.setSize(800, 600);
window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
window.getContentPane().setBackground(Color.MAGENTA); //you can't change color w/o .getContentPane()
window.setLayout(null); //set it to null now (the default), so that you can customize the layout later
window.setVisible(true);
window.setTitle("THE ROOM");
container = window.getContentPane();
titleNamePanel = new JPanel();
titleNamePanel.setBounds(10, 100, 800, 150);
titleNamePanel.setBackground(Color.MAGENTA);
titleNameLabel = new JLabel("THE ROOM");
container.add(titleNamePanel);
titleNamePanel.add(titleNameLabel);
titleNameLabel.setFont(new java.awt.Font("Arial", Font.BOLD, 120));
titleNameLabel.setOpaque(true);
titleNameLabel.setBackground(Color.MAGENTA);
titleNameLabel.setForeground(Color.WHITE);
startButton = new JButton();
startButton.setText("START");
startButton.setFont(new java.awt.Font("Arial", Font.BOLD, 50));
startButton.setBounds(300, 300, 200, 100);
startButton.addActionListener(handler);
container.add(startButton);
}
public void createGameScreen() {
titleNamePanel.setVisible(false);
startButton.setVisible(false);
go_northButtonPanel = new JPanel();
go_northButtonPanel.setBounds(300,400,200,100);
go_northButtonPanel.setBackground(Color.MAGENTA);
go_north = new JButton();
go_north.setBackground(Color.BLACK);
go_north.setForeground(Color.BLACK);
go_north.setFont(new java.awt.Font("Arial", Font.BOLD, 25));
go_north.setBounds(300, 300, 200, 100);
go_north.addActionListener(handler1A);
go_northButtonPanel.add(go_north);
go_north.setText("GO NORTH");
container.add(go_northButtonPanel);
westButtonPanel = new JPanel();
westButtonPanel.setBounds(300,500,200,200);
westButtonPanel.setBackground(Color.MAGENTA);
container.add(westButtonPanel);
west = new JButton();
west.setBackground(Color.BLACK);
west.setForeground(Color.BLACK);
west.setFont(new java.awt.Font("Arial", Font.BOLD, 15));
west.setBounds(300, 500, 200, 200);
west.addActionListener(handler1B);
westButtonPanel.add(west);
west.setText("GO WEST");
textPanel1A = new JPanel();
textPanel1A.setBounds(0,100,800,850);
textPanel1A.setBackground(Color.MAGENTA);
container.add(textPanel1A);
TextArea1A = new JTextArea("You wake up in a small, cell-like room. Where are you? Who are you? You don't remember anything, but all you know is that you're trapped inside this room and you need to ESCAPE.");
TextArea1A.setBounds(0,100,800,850);
TextArea1A.setBackground(Color.MAGENTA);
TextArea1A.setForeground(Color.BLACK);
TextArea1A.setFont(new java.awt.Font("Arial", Font.PLAIN, 20));
TextArea1A.setLineWrap(true);
TextArea1A.setWrapStyleWord(true);
textPanel1A.add(TextArea1A);
}
public void createGameScreen2A() {
go_northButtonPanel.setVisible(false);
westButtonPanel.setVisible(false);
west.setVisible(false);
textPanel1A.setVisible(false);
TextArea1A.setVisible(false);
lift_paintingButtonPanel = new JPanel();
lift_paintingButtonPanel.setBounds(300,400,200,100);
lift_paintingButtonPanel.setBackground(Color.MAGENTA);
lift_painting = new JButton();
lift_painting.setBackground(Color.BLACK);
lift_painting.setForeground(Color.BLACK);
lift_painting.setFont(new java.awt.Font("Arial", Font.BOLD, 25));
lift_painting.setBounds(300, 300, 200, 100);
//lift_painting.addActionListener(handler1A);
lift_paintingButtonPanel.add(lift_painting);
lift_painting.setText("LIFT PAINTING");
container.add(lift_paintingButtonPanel);
go_west_insteadButtonPanel = new JPanel();
go_west_insteadButtonPanel.setBounds(300,500,200,200);
go_west_insteadButtonPanel.setBackground(Color.MAGENTA);
go_west_instead = new JButton();
go_west_instead.setBackground(Color.BLACK);
go_west_instead.setForeground(Color.BLACK);
go_west_instead.setFont(new java.awt.Font("Arial", Font.BOLD, 25));
go_west_instead.setBounds(300, 500, 200, 100);
go_west_insteadButtonPanel.add(go_west_instead);
go_west_instead.setText("GO WEST");
container.add(go_west_insteadButtonPanel);
textPanel2A = new JPanel();
textPanel2A.setBounds(0,100,800,850);
textPanel2A.setBackground(Color.MAGENTA);
container.add(textPanel2A);
TextArea2A = new JTextArea("You wake up in a small, cell-like room. Where are you? Who are you? You don't remember anything, but all you know is that you're trapped inside this room and you need to ESCAPE.");
TextArea2A.setBounds(0,100,800,850);
TextArea2A.setBackground(Color.MAGENTA);
TextArea2A.setForeground(Color.BLACK);
TextArea2A.setFont(new java.awt.Font("Arial", Font.PLAIN, 20));
TextArea2A.setLineWrap(true);
TextArea2A.setWrapStyleWord(true);
textPanel2A.add(TextArea2A);
}
public void createGameScreen2B() {
lift_paintingButtonPanel.setVisible(false); //LINE 190, where the code stops working
go_west_insteadButtonPanel.setVisible(false);
go_west_instead.setVisible(false);
textPanel2A.setVisible(false);
TextArea2A.setVisible(false);
lift_mattressButtonPanel = new JPanel();
lift_mattressButtonPanel.setBounds(300,400,200,100);
lift_mattressButtonPanel.setBackground(Color.MAGENTA);
lift_mattress = new JButton();
lift_mattress.setBackground(Color.BLACK);
lift_mattress.setForeground(Color.BLACK);
lift_mattress.setFont(new java.awt.Font("Arial", Font.BOLD, 25));
lift_mattress.setBounds(300, 300, 200, 100);
//lift_mattress.addActionListener(handler2B);
lift_mattressButtonPanel.add(lift_mattress);
lift_mattress.setText("LIFT PAINTING");
container.add(lift_mattressButtonPanel);
}
public class TitleScreenHandler implements ActionListener {
public void actionPerformed(ActionEvent event) {
createGameScreen();
}
}
public class Screen1AHandler implements ActionListener {
public void actionPerformed(ActionEvent event) {
createGameScreen2A();
}
}
public class Screen1BHandler implements ActionListener {
public void actionPerformed(ActionEvent event) {
createGameScreen2B(); //LINE 225
}
}
}
Stack trace:
Thread [AWT-EventQueue-0] (Suspended)
The_Room.createGameScreen2B() line: 190
The_Room$Screen1BHandler.actionPerformed(ActionEvent) line: 225
JButton(AbstractButton).fireActionPerformed(ActionEvent) line: 1967
AbstractButton$Handler.actionPerformed(ActionEvent) line: 2308
DefaultButtonModel.fireActionPerformed(ActionEvent) line: 405
DefaultButtonModel.setPressed(boolean) line: 262
AquaButtonUI$AquaButtonListener(BasicButtonListener).mouseReleased(MouseEvent) line: 279
JButton(Component).processMouseEvent(MouseEvent) line: 6632
JButton(JComponent).processMouseEvent(MouseEvent) line: 3342
JButton(Component).processEvent(AWTEvent) line: 6397
JButton(Container).processEvent(AWTEvent) line: 2263
JButton(Component).dispatchEventImpl(AWTEvent) line: 5008
JButton(Container).dispatchEventImpl(AWTEvent) line: 2321
JButton(Component).dispatchEvent(AWTEvent) line: 4840
LightweightDispatcher.retargetMouseEvent(Component, int, MouseEvent) line: 4918
LightweightDispatcher.processMouseEvent(MouseEvent) line: 4547
LightweightDispatcher.dispatchEvent(AWTEvent) line: 4488
JFrame(Container).dispatchEventImpl(AWTEvent) line: 2307
JFrame(Window).dispatchEventImpl(AWTEvent) line: 2772
JFrame(Component).dispatchEvent(AWTEvent) line: 4840
EventQueue.dispatchEventImpl(AWTEvent, Object) line: 772
EventQueue$4.run() line: 721
EventQueue$4.run() line: 715
AccessController.doPrivileged(PrivilegedAction<T>, AccessControlContext) line: not available [native method]
ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(PrivilegedAction<T>, AccessControlContext, AccessControlContext) line: 85
ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(PrivilegedAction<T>, AccessControlContext) line: 95
EventQueue$5.run() line: 745
EventQueue$5.run() line: 743
AccessController.doPrivileged(PrivilegedAction<T>, AccessControlContext) line: not available [native method]
ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(PrivilegedAction<T>, AccessControlContext, AccessControlContext) line: 85
EventQueue.dispatchEvent(AWTEvent) line: 742
EventDispatchThread.pumpOneEventForFilters(int) line: 203
EventDispatchThread.pumpEventsForFilter(int, Conditional, EventFilter) line: 124
EventDispatchThread.pumpEventsForHierarchy(int, Conditional, Component) line: 113
EventDispatchThread.pumpEvents(int, Conditional) line: 109
EventDispatchThread.pumpEvents(Conditional) line: 101
EventDispatchThread.run() line: 90
我看到您已经修复了代码，但是我想告诉您，您的类和变量的命名不符合Java约定。尽管这不会导致编译错误，但确实会使您的代码在其他Java开发人员中可读性降低，并且如果您想成为专业（java）开发人员，则绝对应该更改此内容。您现在在某些位置正确执行此操作，而在下一行错误地执行此操作。
所有变量名都应使用驼峰式。所以没有下划线。例如goNorthButtonPanel。我们仅在常量（静态final）中使用下划线，并且这些下划线应全部为大写（例如SOME_CONSTANT_VALUE）。类名应始终以大写字母开头，并且也应使用大写字母，因此不能使用下划线（TheRoom）。您所有方法的名称都是正确的，因此请继续努力：)
有关所有Java约定的概述，请参见https://www.oracle.com/java/technologies/javase/codeconventions-namingconventions.html
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