JComboBox 常用方法示例

准备工作

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

JComboBox<String> jcb = new JComboBox<>();
jcb.addItem("北京");
jcb.addItem("上海");
jcb.addItem("广州");
jcb.addItem("深圳");

---

1. addItem() — 添加选项

JComboBox<String> jcb = new JComboBox<>();
jcb.addItem("北京");
jcb.addItem("上海");
jcb.addItem("广州");

System.out.println("选项数量：" + jcb.getItemCount());

输出：
选项数量：3

---

2. getItemCount() — 获取选项总数

JComboBox<String> jcb = new JComboBox<>();
jcb.addItem("北京");
jcb.addItem("上海");
jcb.addItem("广州");

System.out.println(jcb.getItemCount());

输出：
3

---

3. getItemAt() — 获取指定下标的选项

JComboBox<String> jcb = new JComboBox<>();
jcb.addItem("北京");
jcb.addItem("上海");
jcb.addItem("广州");

System.out.println(jcb.getItemAt(0));
System.out.println(jcb.getItemAt(1));
System.out.println(jcb.getItemAt(2));

输出：
北京
上海
广州

---

4. getSelectedItem() — 获取当前选中项

JComboBox<String> jcb = new JComboBox<>();
jcb.addItem("北京");
jcb.addItem("上海");
jcb.addItem("广州");

// 默认选中第一项
System.out.println(jcb.getSelectedItem());

输出：
北京

---

5. getSelectedIndex() — 获取当前选中项的下标

JComboBox<String> jcb = new JComboBox<>();
jcb.addItem("北京");
jcb.addItem("上海");
jcb.addItem("广州");

System.out.println(jcb.getSelectedIndex());

输出：
0

---

6. setSelectedIndex() — 设置选中项

JComboBox<String> jcb = new JComboBox<>();
jcb.addItem("北京");
jcb.addItem("上海");
jcb.addItem("广州");

jcb.setSelectedIndex(2); // 选中第2项
System.out.println(jcb.getSelectedItem());

输出：
广州

---

7. setSelectedItem() — 按内容设置选中项

JComboBox<String> jcb = new JComboBox<>();
jcb.addItem("北京");
jcb.addItem("上海");
jcb.addItem("广州");

jcb.setSelectedItem("上海");
System.out.println(jcb.getSelectedIndex());

输出：
1

---

8. removeItem() — 删除指定选项

JComboBox<String> jcb = new JComboBox<>();
jcb.addItem("北京");
jcb.addItem("上海");
jcb.addItem("广州");

jcb.removeItem("上海");
System.out.println(jcb.getItemCount());
System.out.println(jcb.getItemAt(0));
System.out.println(jcb.getItemAt(1));

输出：
2
北京
广州

---

9. removeItemAt() — 删除指定下标的选项

JComboBox<String> jcb = new JComboBox<>();
jcb.addItem("北京");
jcb.addItem("上海");
jcb.addItem("广州");

jcb.removeItemAt(0); // 删除第0项
System.out.println(jcb.getItemAt(0));

输出：
上海

---

10. removeAllItems() — 清空所有选项

JComboBox<String> jcb = new JComboBox<>();
jcb.addItem("北京");
jcb.addItem("上海");
jcb.addItem("广州");

jcb.removeAllItems();
System.out.println(jcb.getItemCount());

输出：
0

---

11. setEditable() — 设置是否可编辑

JComboBox<String> jcb = new JComboBox<>();
jcb.addItem("北京");
jcb.addItem("上海");

jcb.setEditable(true); // 允许用户手动输入
System.out.println(jcb.isEditable());

输出：
true

---

12. setEnabled() — 设置是否可用

JComboBox<String> jcb = new JComboBox<>();
jcb.addItem("北京");
jcb.addItem("上海");

jcb.setEnabled(false); // 禁用下拉框，用户无法操作
System.out.println(jcb.isEnabled());

输出：
false

---

13. addActionListener() — 监听选项变化

JComboBox<String> jcb = new JComboBox<>();
jcb.addItem("北京");
jcb.addItem("上海");
jcb.addItem("广州");

jcb.addActionListener(e -> {
    String selected = (String) jcb.getSelectedItem();
    System.out.println("当前选中：" + selected);
});

// 模拟选择操作
jcb.setSelectedIndex(1);
jcb.setSelectedIndex(2);

输出：
当前选中：上海
当前选中：广州

---

14. 完整窗口示例

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

public class Demo {
    public static void main(String[] args) {
        JFrame jf = new JFrame("JComboBox 示例");
        jf.setLayout(new FlowLayout());
        jf.setSize(300, 200);
        jf.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

        JComboBox<String> jcb = new JComboBox<>();
        jcb.addItem("北京");
        jcb.addItem("上海");
        jcb.addItem("广州");
        jcb.addItem("深圳");

        JLabel label = new JLabel("当前选中：北京");

        // 选项变化时更新标签
        jcb.addActionListener(e -> {
            label.setText("当前选中：" + jcb.getSelectedItem());
        });

        jf.add(jcb);
        jf.add(label);
        jf.setVisible(true);
    }
}

---

API 速查表

方法	说明	返回值
addItem(E item)	添加选项	void
getItemCount()	获取选项总数	int
getItemAt(int index)	获取指定下标的选项	E
getSelectedItem()	获取当前选中项	Object
getSelectedIndex()	获取当前选中项下标	int
setSelectedIndex(int index)	按下标设置选中项	void
setSelectedItem(Object item)	按内容设置选中项	void
removeItem(Object item)	删除指定选项	void
removeItemAt(int index)	删除指定下标选项	void
removeAllItems()	清空所有选项	void
setEditable(boolean b)	设置是否可编辑	void
isEditable()	是否可编辑	boolean
setEnabled(boolean b)	设置是否可用	void
isEnabled()	是否可用	boolean
addActionListener(...)	监听选项变化	void