Java Swing 選項組件全解析：JCheckBox、JRadioButton 與 ButtonGroup

組件類型對比

建構子速查

// JCheckBox
new JCheckBox()
new JCheckBox(String text)
new JCheckBox(String text, boolean selected)
new JCheckBox(Icon icon)
new JCheckBox(String text, Icon icon, boolean selected)

// JRadioButton (參數相同)
new JRadioButton()
new JRadioButton(String text)
new JRadioButton(String text, boolean selected)

ButtonGroup：實現單選邏輯

ButtonGroup 本身不顯示，僅管理一組按鈕的互斥狀態。

ButtonGroup group = new ButtonGroup();
JRadioButton r1 = new JRadioButton("選項 A");
JRadioButton r2 = new JRadioButton("選項 B");
JRadioButton r3 = new JRadioButton("選項 C");
group.add(r1); group.add(r2); group.add(r3);
// 程式預選
r2.setSelected(true);
// 取得目前選中的模型
ButtonModel selected = group.getSelection();

事件處理：ItemListener vs ActionListener

• ItemListener：itemStateChanged(ItemEvent e)，可區分 SELECTED/DESELECTED，適合核取方塊。
• ActionListener：actionPerformed(ActionEvent e)，僅在按鈕被點擊（狀態改變）觸發，適合單選按鈕。

完整範例：產品選購介面

package swing.demo;

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

public class ProductSelector extends JFrame implements ItemListener {
    // 單選：品牌
    private JRadioButton rbDell, rbHp, rbLenovo;
    private ButtonGroup brandGroup;
    // 核取：配件
    private JCheckBox cbMouse, cbBag, cbWarranty;
    // 顯示區
    private JTextArea logArea;

    public ProductSelector() {
        setTitle("產品選購示範");
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLayout(new BorderLayout(10,10));

        // 品牌面板
        JPanel brandPanel = new JPanel(new GridLayout(0,1));
        brandPanel.setBorder(BorderFactory.createTitledBorder("品牌 (單選)"));
        brandGroup = new ButtonGroup();
        rbDell = createRadio("Dell", brandPanel, brandGroup);
        rbHp = createRadio("HP", brandPanel, brandGroup);
        rbLenovo = createRadio("Lenovo", brandPanel, brandGroup);
        rbDell.setSelected(true);

        // 配件面板
        JPanel accPanel = new JPanel(new GridLayout(0,1));
        accPanel.setBorder(BorderFactory.createTitledBorder("配件 (多選)"));
        cbMouse = createCheck("滑鼠", accPanel);
        cbBag = createCheck("筆電包", accPanel);
        cbWarranty = createCheck("延保服務", accPanel);

        // 顯示區
        logArea = new JTextArea(8, 30);
        logArea.setEditable(false);
        JScrollPane scroll = new JScrollPane(logArea);

        // 佈局
        JPanel left = new JPanel(new GridLayout(2,1,5,5));
        left.add(brandPanel);
        left.add(accPanel);
        add(left, BorderLayout.WEST);
        add(scroll, BorderLayout.CENTER);

        pack();
        setLocationRelativeTo(null);
    }

    private JRadioButton createRadio(String text, Container parent, ButtonGroup group) {
        JRadioButton rb = new JRadioButton(text);
        rb.addItemListener(this);
        group.add(rb);
        parent.add(rb);
        return rb;
    }

    private JCheckBox createCheck(String text, Container parent) {
        JCheckBox cb = new JCheckBox(text);
        cb.addItemListener(this);
        parent.add(cb);
        return cb;
    }

    @Override
    public void itemStateChanged(ItemEvent e) {
        Object src = e.getItemSelectable();
        String action = (e.getStateChange() == ItemEvent.SELECTED) ? "選取" : "取消";
        StringBuilder sb = new StringBuilder();
        sb.append("[").append(action).append("] ");

        if (src == rbDell) sb.append("品牌：Dell");
        else if (src == rbHp) sb.append("品牌：HP");
        else if (src == rbLenovo) sb.append("品牌：Lenovo");
        else if (src == cbMouse) sb.append("配件：滑鼠");
        else if (src == cbBag) sb.append("配件：筆電包");
        else if (src == cbWarranty) sb.append("配件：延保服務");

        logArea.append(sb.toString() + "\n");
        logArea.setCaretPosition(logArea.getDocument().getLength());
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> new ProductSelector().setVisible(true));
    }
}

常見錯誤

1. 忘記將 JRadioButton 加入 ButtonGroup → 變成可多選。
2. 在同一個 ButtonGroup 中混入 JCheckBox → 邏輯混亂，勿如此做。
3. 使用 ActionListener 監聽 JCheckBox → 無法區分勾選/取消，改用 ItemListener。

總結

JCheckBox 對應「獨立開關」，JRadioButton + ButtonGroup 對應「互斥單選」。善用 ItemListener 獲取狀態變化細節，配合邊框標題與佈局管理器，可快速建構清晰的選項介面。