半透明のスイング コンポーネントを適切に再ペイントするにはどうすればよいですか?

import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JLabel;

public class TranslucentJLabel extends JLabel {

    public TranslucentJLabel() {
        setOpaque(false);
        setBackground(new Color(0f, 0f, 0f, 0.5f));
        setFont(new Font("Serif", Font.PLAIN, 48));
    }

    @Override
    protected void paintComponent(Graphics g) {
        Graphics2D g2d = (Graphics2D) g;
        g2d.setComposite(AlphaComposite.SrcOver);
        super.paintComponent(g2d);
    }

}

import java.awt.AlphaComposite;
import java.awt.Color;
import javax.swing.JFrame;

public class TranslucentFrame extends JFrame {

    public TranslucentFrame() {
        setBackground(new Color(0f, 0f, 0f, 0.7f));
        setUndecorated(true);
        setSize(300, 200);
        setLocationRelativeTo(null);
        setVisible(true);
    }

    @Override
    public void paint(Graphics g) {
        Graphics2D g2d = (Graphics2D) g;
        g2d.setComposite(AlphaComposite.SrcOver);
        super.paint(g2d);
    }
}