解決跨平台、多分辨率、動態調整下組件位置與大小的自適應問題。Swing/AWT提供7大佈局，覆蓋從簡單到複雜的所有UI構建需求。
| 佈局 | 核心特性 | 適用場景 | 關鍵API | 優點 | 缺點 |
|---|---|---|---|---|---|
| FlowLayout | 流式排列，左右/居中/右對齊，超寬自動換行 | 工具欄、按鈕組、簡單表單 | new FlowLayout(align, hgap, vgap) | 簡單、自動換行、響應式 | 精確控制困難、組件大小固定 |
| BorderLayout | 五大區域：NORTH/SOUTH/EAST/WEST/CENTER，邊緣組件按優先尺寸，中間填滿 | 主窗體骨架：頂部導航、底部狀態、側邊欄、中心內容 | add(comp, BorderLayout.CENTER) | 經典框架結構、語義清晰 | 僅容納5組件、嵌套較繁瑣 |
| GridLayout | 矩陣網格，行列固定，組件等分空間 | 計算器鍵盤、棋盤、表格式輸入 | new GridLayout(rows, cols, hgap, vgap) | 規則整齊、代碼極簡 | 無法跨行列合併、組件強制等大 |
| GridBagLayout | 網格包，組件可跨行列、錨點對齊、權重伸縮、內外邊距 | 複雜表單、儀表盤、需精細控制的界面 | GridBagConstraints (gbc) | 最靈活、功能最全、單佈局搞定複雜UI | API繁瑣、學習曲線陡峭、代碼冗長 |
| CardLayout | 卡片疊放，同一時刻僅顯示一張，支持翻頁/跳轉 | 向導頁面、Tab切換、狀態機界面 | show(parent, "cardName") / next()/previous() | 天然支持視圖切換、內存常駐 | 非可見卡片仍佔內存、動畫需自行實現 |
| GroupLayout | 分組佈局，順序組/並行組嵌套，間隙自動管理，IDE可視化設計首選 | 複雜對話框、響應式表單、Matisse/WindowBuilder生成代碼 | createSequentialGroup() / createParallelGroup() | 功能強大、支持基線對齊、IDE友好 | 手寫代碼極難維護、幾乎必須依賴GUI設計器 |
public class CalculatorUI extends JFrame {
public CalculatorUI() {
setTitle("計算器");
setDefaultCloseOperation(EXIT_ON_CLOSE);
setLayout(new BorderLayout(5, 5));
// 北部：顯示屏
JTextField display = new JTextField();
display.setEditable(false);
display.setHorizontalAlignment(JTextField.RIGHT);
display.setFont(new Font("Monospaced", Font.BOLD, 24));
add(display, BorderLayout.NORTH);
// 中部：按鍵盤 (4行 x 4列)
JPanel keypad = new JPanel(new GridLayout(4, 4, 5, 5));
String[] keys = {
"7", "8", "9", "/",
"4", "5", "6", "*",
"1", "2", "3", "-",
"0", ".", "=", "+"
};
for (String key : keys) {
JButton btn = new JButton(key);
btn.setFont(new Font("SansSerif", Font.BOLD, 18));
keypad.add(btn);
}
add(keypad, BorderLayout.CENTER);
pack();
setLocationRelativeTo(null);
setResizable(false);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(() -> new CalculatorUI().setVisible(true));
}
}
public class FormDemo extends JFrame {
public FormDemo() {
setLayout(new GridBagLayout());
GridBagConstraints gbc = new GridBagConstraints();
gbc.insets = new Insets(5, 5, 5, 5); // 統一邊距
gbc.fill = GridBagConstraints.HORIZONTAL;
gbc.anchor = GridBagConstraints.WEST;
// 第1行：用戶名
gbc.gridx = 0; gbc.gridy = 0; gbc.weightx = 0;
add(new JLabel("用戶名:"), gbc);
gbc.gridx = 1; gbc.weightx = 1.0; // 輸入框佔滿剩餘寬度
JTextField username = new JTextField(20);
add(username, gbc);
// 第2行：密碼
gbc.gridx = 0; gbc.gridy = 1; gbc.weightx = 0;
add(new JLabel("密碼:"), gbc);
gbc.gridx = 1; gbc.weightx = 1.0;
JPasswordField password = new JPasswordField(20);
add(password, gbc);
// 第3行：跨列按鈕
gbc.gridx = 0; gbc.gridy = 2; gbc.gridwidth = 2; // 跨2列
gbc.fill = GridBagConstraints.NONE;
gbc.anchor = GridBagConstraints.CENTER;
JPanel btnPanel = new JPanel(new FlowLayout(FlowLayout.CENTER, 10, 0));
btnPanel.add(new JButton("登錄"));
btnPanel.add(new JButton("註冊"));
add(btnPanel, gbc);
pack();
}
}
public class WizardDemo extends JFrame {
private CardLayout cardLayout = new CardLayout();
private JPanel cardPanel = new JPanel(cardLayout);
public WizardDemo() {
add(cardPanel);
// 三張卡片
cardPanel.add(createStep1(), "step1");
cardPanel.add(createStep2(), "step2");
cardPanel.add(createStep3(), "step3");
// 底部導航欄
JPanel nav = new JPanel();
JButton prev = new JButton("上一步");
JButton next = new JButton("下一步");
JButton finish = new JButton("完成");
nav.add(prev); nav.add(next); nav.add(finish);
add(nav, BorderLayout.SOUTH);
prev.addActionListener(e -> cardLayout.previous(cardPanel));
next.addActionListener(e -> cardLayout.next(cardPanel));
finish.addActionListener(e -> dispose());
pack();
}
private JPanel createStep1() { /* 返回面板 */ }
private JPanel createStep2() { /* 返回面板 */ }
private JPanel createStep3() { /* 返回面板 */ }
}
Swing/AWT屬於維護模式，新項目建議：
佈局管理器是GUI開發的「骨架」。掌握Flow/Border/Grid三基礎佈局可應對80%簡單界面；GridBagLayout是瑞士軍刀，解決疑難雜症；CardLayout專治視圖切換；GroupLayout留給設計器生成。新項目優先考慮JavaFX/Compose/Web現代棧，Swing僅作維舊項目或嵌入式場景選擇。
