Java Swing 半透明視窗實作：AWTUtilities 與 JDK 7+ 標準 API 對比

舊版做法（JDK 6u10+，內部 API）

import com.sun.awt.AWTUtilities;
public class TranslucentFrame extends JFrame {
    public TranslucentFrame() {
        AWTUtilities.setWindowOpacity(this, 0.6f); // 0.0~1.0
        setTitle("半透明視窗");
        setSize(400, 300);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
        setVisible(true);
    }
    public static void main(String[] args) { new TranslucentFrame(); }
}

缺點： com.sun.* 非標準，JDK 9+ 模組化後默認不可訪問，需 --add-opens。

標準做法（JDK 7+）

public class TranslucentFrame extends JFrame {
    public TranslucentFrame() {
        // 必須在 setVisible 前設置，且需底層視窗系統支援
        setBackground(new Color(0, 0, 0, 0)); // 透明背景
        setUndecorated(true); // 去除標題欄/邊框（可選）

        // 整體不透明度
        setOpacity(0.6f); 

        setTitle("標準半透明視窗");
        setSize(400, 300);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
        setVisible(true);
    }
}

進階：非矩形/漸變透明視窗

// 形狀：圓角矩形
setShape(new RoundRectangle2D.Double(0, 0, 400, 300, 30, 30));

// 漸變透明：需重寫 paintComponent
JPanel panel = new JPanel() {
    @Override protected void paintComponent(Graphics g) {
        Graphics2D g2 = (Graphics2D) g.create();
        g2.setPaint(new GradientPaint(0, 0, new Color(0,0,0,0.8f), 
                                      0, 300, new Color(0,0,0,0f)));
        g2.fillRect(0, 0, getWidth(), getHeight());
        g2.dispose();
    }
};
panel.setOpaque(false);
setContentPane(panel);

支援度檢測

GraphicsDevice gd = GraphicsEnvironment.getLocalGraphicsEnvironment().getDefaultScreenDevice();
boolean translucent = gd.isWindowTranslucencySupported(GraphicsDevice.WindowTranslucency.TRANSLUCENT);
boolean perPixel = gd.isWindowTranslucencySupported(GraphicsDevice.WindowTranslucency.PERPIXEL_TRANSLUCENT);
System.out.println("整體透明: " + translucent + ", 像素級: " + perPixel);

注意事項