import java.awt.Color;
import java.awt.Component;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class TransparentPanel {
    TPanel lowerPanel, upperPanel;

    public TransparentPanel() {
        initGUI();
    }

    private void initGUI() {
        JFrame frame = new JFrame("Teiltransparentes JPanel");
        frame.setSize(300, 300);

        lowerPanel = new TPanel("Ein Text im unteren Panel",
                new Color(0f, 0f, 1f, 0.5f), new Color(1f, 1f, 0f, 0.6f), 300,
                300, frame);
        
        Dimension ldim = new Dimension(frame.getWidth(), frame.getHeight());
        lowerPanel.setPreferredSize(ldim);
        lowerPanel.setMinimumSize(ldim);
        lowerPanel.setSize(ldim);

        upperPanel = new TPanel("Ein oberer Text", new Color(1f, 0f, 0f, 0.6f),
                new Color(0f, 0f, 0f, 0.4f), 200, 200, frame);
        Dimension udim = new Dimension(frame.getWidth() - 60, frame.getHeight() - 60);
        upperPanel.setPreferredSize(udim);
        upperPanel.setMinimumSize(udim);
        upperPanel.setSize(udim);

        frame.setLayout(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.anchor = GridBagConstraints.NORTHWEST;
        add(upperPanel, gbc, 1, 1, 1, 1, frame);
        add(lowerPanel, gbc, 1, 1, 1, 1, frame);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public void add(Component c, GridBagConstraints constraints, int x, int y,
            int w, int h, Container p) {
        constraints.gridx = x;
        constraints.gridy = y;
        constraints.gridwidth = w;
        constraints.gridheight = h;
        p.add(c, constraints);
    }

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

class TPanel extends JPanel {
    String txt;
    Color fgColor, bgColor;
    int width, height;
    Component parent;

    public TPanel(int width, int height, Component parent) {
        this("", parent.getBackground(), parent.getForeground(), width, height,
                parent);
    }

    public TPanel(String txt, Color bgColor, Color fgColor, int width,
            int height, Component parent) {
        this.txt = txt;
        this.fgColor = fgColor;
        this.bgColor = bgColor;
        this.width = width;
        this.height = height;
        this.parent = parent;
        setOpaque(false);
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(bgColor);
        int start = (parent.getWidth() - width) / 2;
        g.fillRect(start, start, width, height);
        g.setColor(fgColor);
        g.setFont(new Font("Verdana", Font.BOLD, 20));
        for (int i = 0; i < 15; ++i) {
            g.drawString(txt + "\n", start + 5, start + 20 + i * 20);
        }
    }
}