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我正在嘗試創建一個編寫電子郵件消息的應用程序。當發送按鈕被按下時，應用程序打印出用戶輸入的收件人，抄送，密送，主題和消息。由於某些原因，當按鈕被按下時，它給了我一個錯誤「在線程異常‘的AWT - EventQueue的 - 0’ 這裏是我的代碼：爲編寫電子郵件消息創建GUI
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class EmailWindow extends JPanel {
private JTextField to, cc, bcc, subject;
private JTextPane content;
private JButton send;
public EmailWindow() {
// Construct and add text fields for to, cc, bcc, and subject, followed
// by a Send button. You may use the createComponentWithLabel(...)
// utility method to construct a panel that includes a label and
// a text field, which can then be added to the EmailWindow panel.
// For example,
// add(createComponentWithLabel("Text", new JTextField(30));
// would add a text field next to a label with the word "Text".
add(createComponentWithLabel("to", new JTextField(30)));
add(createComponentWithLabel("cc", new JTextField(30)));
add(createComponentWithLabel("bcc", new JTextField(30)));
add(createComponentWithLabel("subject", new JTextField(30)));
// The JTextPane class supports multi-line text. For a single line
// of content text, you could use another JTextField instead.
setBackground(Color.cyan);
content = new JTextPane();
content.setPreferredSize(new Dimension(375, 200));
send = new JButton("Send");
send.addActionListener(new SendListener());
add(content);
add(send);
}
// -----------------------------------------------------------------------
// Utility method (which you may use in the constructor) that creates
// and returns a <code>JPanel</code> containing a <code>JLabel</code>
// next to an arbitrary component, such as a <code>JTextField</code>.
// -----------------------------------------------------------------------
private JPanel createComponentWithLabel(String label, Component comp) {
JPanel p = new JPanel();
p.setLayout(new BorderLayout());
p.add(new JLabel(label, JLabel.RIGHT), BorderLayout.WEST);
p.add(comp, BorderLayout.CENTER);
return p;
}
// -----------------------------------------------------------------------
// Listener class to be attached to the Send button. When the button
// is pressed, the contents of the to, cc, bcc, subject, and contents
// fields will be printed to standard out.
// -----------------------------------------------------------------------
private class SendListener implements ActionListener {
public void actionPerformed(ActionEvent evt) {
System.out.println("To: " + to.getText());
System.out.println("Cc: " + cc.getText());
System.out.println("Bcc: " + bcc.getText());
System.out.println("Subject: " + subject.getText());
System.out.println("Message content: "+content.getText());
System.out.println(content.getText());
}
}
}
主要類：
import javax.swing.JFrame;
public class email {
public static void main(String[] args) {
// TODO Auto-generated method stub
// Create a frame
JFrame frame = new JFrame("Compose Message");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// Create an instance of EmailWindow and add it to the frame.
EmailWindow email = new EmailWindow();
frame.getContentPane().add(email);
// Set a reasonable starting size for the frame. Note that we
// do not use pack() here, since doing so with the default layout
// manager would produce a very long frame. Other layout managers
// (which will be discussed in Chapter 6) would solve this problem
// in a more flexible way.
frame.setSize(425, 400);
// Show the frame.
frame.setVisible(true);
}
}
錯誤：
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at hw6.EmailWindow$SendListener.actionPerformed(EmailWindow.java:59)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$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$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.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)
請張貼異常的完整堆棧跟蹤。 – Berger
添加異常 – begincoding123