jcombobox用法

JComboBox是Java Swing库中的一个组件，它可以让用户从下拉菜单中选择一个选项。下面是JComboBox的基本用法：

1. 创建JComboBox对象：

JComboBox comboBox = new JComboBox();

2. 添加选项：

comboBox.addItem("Option 1");
comboBox.addItem("Option 2");
comboBox.addItem("Option 3");

3. 设置默认选项：

comboBox.setSelectedIndex(0); // 默认选择第一项

4. 监听选择事件：

comboBox.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {
        JComboBox comboBox = (JComboBox) e.getSource();
        String selectedOption = (String) comboBox.getSelectedItem();
        // 处理选择事件
    }
});

完整示例代码：

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

public class ComboBoxDemo implements ActionListener {
    JComboBox comboBox;
    
    public ComboBoxDemo() {
        JFrame frame = new JFrame("ComboBox Demo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        comboBox = new JComboBox();
        comboBox.addItem("Option 1");
        comboBox.addItem("Option 2");
        comboBox.addItem("Option 3");
        comboBox.setSelectedIndex(0);
        comboBox.addActionListener(this);
        
        frame.add(comboBox);
        frame.pack();
        frame.setVisible(true);
    }
    
    public void actionPerformed(ActionEvent e) {
        JComboBox comboBox = (JComboBox) e.getSource();
        String selectedOption = (String) comboBox.getSelectedItem();
        System.out.println("Selected option: " + selectedOption);
    }
    
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new ComboBoxDemo();
            }
        });
    }
}