为什么我的程序编译但是没有运行？

Question

由于对OP代码进行了更改,这是一个后续问题.另一位用户建议我将另一个问题与此问题联系起来.

OP是:为什么即使没有任何错误,编译器也不运行程序？

我有一个编译的代码,但它没有运行.我试图让GUI运行,以便我可以添加代码来执行我需要它的功能.代码如下:

import java.awt.*;
import javax.swing.*;

import java.awt.event.*;

public class Transaction extends JFrame {

private static final long serialVersionUID = 1L;
// JFrame frame = new JFrame("Bank Account - S Standridge");
JMenuBar menuBar;
JMenu file = new JMenu("File");
JMenu edit = new JMenu("Edit");
JMenu about = new JMenu("About");
JMenuItem transaction = new JMenuItem("Transaction");
JMenuItem summary = new JMenuItem("Summary");
JMenuItem exit = new JMenuItem("Exit");
private JPanel mp;
private JPanel tp;
private JPanel bp;
private JButton calcButton;    
private JButton exitButton; 
private JMenuItem summaryMenuItem;
private JMenuItem aboutMenuItem;
private JMenuItem exitMenuItem;

public Transaction() {
    setTitle("Bank Account - S Standridge");

    mp = new JPanel();
    tp = new JPanel();
    bp = new JPanel();

    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    setLayout(new BorderLayout());

    menuPanel();        
    transactionPanel();
    BuildButtonPanel();     

    add(mp, BorderLayout.NORTH);
    add(tp, BorderLayout.WEST);
    add(bp, BorderLayout.SOUTH);

    pack();
    setVisible(true);
}

public void summary() {

}

private void menuPanel() {
    b
    menuBar = new JMenuBar();

    setJMenuBar(menuBar);
    setVisible(true);

    menuBar.add(file);
    menuBar.add(edit);
    menuBar.add(about);

    summaryMenuItem.addActionListener(new SummaryMenuListener());
    aboutMenuItem.addActionListener(new AboutMenuListener());

    file.add(transaction);
    file.add(summaryMenuItem);
    file.add(exitMenuItem);


}

private void BuildButtonPanel() {

     // Create a panel for the buttons.
      bp = new JPanel();

      // Create the buttons.
      calcButton = new JButton("Calculate");
      exitButton = new JButton("Exit");

      // Register the action listeners.
      calcButton.addActionListener(new CalcButtonListener());
      exitButton.addActionListener(new ExitButtonListener());

      // Add the buttons to the button panel.
      bp.add(calcButton);
      bp.add(exitButton);

}

private void transactionPanel()
{
    setLayout(new FlowLayout());

    JRadioButton b1 = new JRadioButton("Checkings");
    // b1.addActionListener(this);
    add(b1);

    JRadioButton b2 = new JRadioButton("Savings");
    // b2.addActionListener(this);
    add(b2);



    ButtonGroup bg = new ButtonGroup();
    bg.add(b1);
    bg.add(b2);


    JTextField tf = new JTextField(5);
    add(tf);
  }

}

class CalcButtonListener implements ActionListener
{
   public void actionPerformed(ActionEvent e)
   {

   }
}

class SummaryMenuListener implements ActionListener
   {
      public void actionPerformed(ActionEvent e)
      {

      }
   }

class ExitButtonListener implements ActionListener
   {
      public void actionPerformed(ActionEvent e)
      {
          System.exit(0);
      }
   }

class AboutMenuListener implements ActionListener
   {
      public void actionPerformed(ActionEvent e)
      {
       // Displays Message Box
      }
   }

我在控制台中遇到的错误如下:

java.lang.reflect.InvocationTargetException
IWAV0052E Invocation Target Exception creating Transaction
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at org.eclipse.ve.internal.java.vce.launcher.remotevm.JFCLauncher$1.run(JFCLauncher.java:59)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$000(Unknown Source)
at java.awt.EventQueue$1.run(Unknown Source)
at java.awt.EventQueue$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$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)
Caused by: java.lang.NullPointerException
at Transaction.menuPanel(Transaction.java:64)
at Transaction.<init>(Transaction.java:37)
... 19 more

Answer 1

嗯,这肯定不是你的实际代码,因为你b在menuPanel方法的开头有一个流氓.但是,您基本上需要查看堆栈跟踪:

Caused by: java.lang.NullPointerException
at Transaction.menuPanel(Transaction.java:64)
at Transaction.<init>(Transaction.java:37)

查看其中的那些行Transaction并找出空指针所在的位置.

看起来就是这条线:

summaryMenuItem.addActionListener(new SummaryMenuListener());

您尚未初始化summaryMenuItem,因此当您尝试在其值上调用方法时,您将获得异常.

比修复这个特定错误更重要的是学习如何修复bug:

• 查看堆栈跟踪
• 了解异常的含义
• 如有必要,在调试器中运行代码,调试器通常会在抛出未捕获的异常时暂停
• 如果可能,编写一个单元测试,以便您可以自信地修复代码