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由於OP代碼發生更改，這是一個跟進問題。另一位用戶建議我將另一個問題與這個問題聯繫起來。爲什麼我的程序編譯但不能運行？
的OP爲：Why does the compiler not run the program even though there are not any errors?
我有一個編譯代碼，但它不運行。我試圖讓GUI運行，以便我可以添加代碼來執行我需要的功能。代碼如下爲：是
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
}
}
我在控制檯中看到的錯誤如下所示：
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
從我可以收集的信息來看，似乎是「抱怨」，因爲actionPerformed方法中沒有任何代碼，summaryMenuItem的動作偵聽器不會執行任何操作。但是，即使我在ActionPerformed塊中放置了一個JOptionPane，我仍然會得到相同的空指針。 – Ryujin89 2011-05-08 09:55:07
NullPointerException意味着您正在嘗試調用某個爲null的方法。這並不意味着你沒有任何代碼。 – Kaj 2011-05-08 09:57:01
在閱讀了@Jon Skeet和@Kaj之後，我能夠進行更改並使代碼正常工作。感謝所有協助過的人。 – Ryujin89 2011-05-08 10:13:07