我尝试从JComboBox
选择案例,然后写一个值并打开该网站"案例+值"。但是,当我点击按钮时收到此错误消息:
Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: java.awt.Button cannot be cast to javax.swing.JComboBox
at Deneme1.actionPerformed(Deneme1.java:52)
at java.awt.Button.processActionEvent(Button.java:409)
at java.awt.Button.processEvent(Button.java:377)
at java.awt.Component.dispatchEventImpl(Component.java:4889)
at java.awt.Component.dispatchEvent(Component.java:4711)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.awt.EventQueue$3.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:80)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:90)
at java.awt.EventQueue$4.run(EventQueue.java:731)
at java.awt.EventQueue$4.run(EventQueue.java:729)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:80)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
有我的源代码:
import java.awt.*;
import java.awt.event.*;
import java.io.IOException;
import java.net.URI;
import javax.swing.*;
import java.net.URISyntaxException;
public class Deneme1 extends Frame implements WindowListener, ActionListener {
JTextField Value = new JTextField(20);
Button Try;
public static void main(String[] args) {
Deneme1 Windows = new Deneme1("Deneme1 ");
Windows.setSize(400, 200);
Windows.setLocation(430, 100);
Windows.setVisible(true);
Windows.setTitle("Title");
}
public Deneme1(String title) {
JLabel Text2 = new JLabel("Pick one: ");
add(Text2);
JComboBox Select = new JComboBox();
Select.addItem("A");
Select.addItem("B");
add(Select);
JLabel Text1 = new JLabel("Enter Value:");
setLayout(new FlowLayout());
addWindowListener(this);
Try = new Button("Try");
add(Text1);
add(Value);
add(Try);
Try.addActionListener(this);
}
public void actionPerformed(ActionEvent E) {
JComboBox<String> Select = (JComboBox<String>) E.getSource();
String Selected = (String) Select.getSelectedItem();
switch (Selected) {
case "A":
try {
URI AcilacakSite = new URI("https://A" + Value.getText());
Desktop.getDesktop().browse(AcilacakSite);
} catch (URISyntaxException | IOException ex) {
JOptionPane.showMessageDialog(null, "ERR");
}
break;
case "B":
try {
URI AcilacakSite = new URI("https://B" + Value.getText());
Desktop.getDesktop().browse(AcilacakSite);
} catch (URISyntaxException | IOException ex) {
JOptionPane.showMessageDialog(null, "ERR");
}
break;
default:
JOptionPane.showMessageDialog(null, "ERR");
break;
}
}
@Override
public void windowOpened(WindowEvent e) {
//throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
}
@Override
public void windowClosing(WindowEvent e) {
dispose();
System.exit(0);
}
@Override
public void windowClosed(WindowEvent e) {
//throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
}
@Override
public void windowIconified(WindowEvent e) {
//throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
}
@Override
public void windowDeiconified(WindowEvent e) {
//throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
}
@Override
public void windowActivated(WindowEvent e) {
//throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
}
@Override
public void windowDeactivated(WindowEvent e) {
//throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
}
}
答案 0 :(得分:2)
此代码通过将组合框声明为类属性并在执行的操作方法中直接访问它来修复ClassCastException
。
import java.awt.*;
import java.awt.event.*;
import java.net.*;
import javax.swing.*;
import java.io.IOException;
public class Deneme1 extends JFrame implements ActionListener {
JTextField value = new JTextField(20);
JButton tryFetch;
// declared as a class attribute, this can be accessed
// in the action performed method
JComboBox select;
public static void main(String[] args) {
Deneme1 windows = new Deneme1("Deneme1 ");
windows.setSize(400, 200);
windows.setLocation(430, 100);
windows.setVisible(true);
windows.setTitle("Title");
}
public Deneme1(String title) {
JLabel text2 = new JLabel("Pick one: ");
add(text2);
select = new JComboBox();
select.addItem("A");
select.addItem("B");
add(select);
JLabel text1 = new JLabel("Enter value:");
setLayout(new FlowLayout());
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
tryFetch = new JButton("Try");
add(text1);
add(value);
add(tryFetch);
tryFetch.addActionListener(this);
}
public void actionPerformed(ActionEvent E) {
String selected = (String) select.getSelectedItem();
switch (selected) {
case "A":
try {
URI AcilacakSite = new URI("https://A" + value.getText());
Desktop.getDesktop().browse(AcilacakSite);
} catch (URISyntaxException | IOException ex) {
JOptionPane.showMessageDialog(null, "ERR");
}
break;
case "B":
try {
URI AcilacakSite = new URI("https://B" + value.getText());
Desktop.getDesktop().browse(AcilacakSite);
} catch (URISyntaxException | IOException ex) {
JOptionPane.showMessageDialog(null, "ERR");
}
break;
default:
JOptionPane.showMessageDialog(null, "ERR");
break;
}
}
}
注意:我修正了问题评论中提到的大部分内容。这段代码仍有问题。