Drawing problem with swing

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Java

Swing

drawing

Hi!
A view weeks ago I changed from Visual Studio C# to Java and now I've tried my first project with Swing and WindowBuilder. So far so good and everything works fine - except drawing that line. There's no error message but also no line. Neither paint(... nor paintComponents(... gets a call. What's wrong?
Thanks.

package Test2GUI;

//import java.time.*;
import java.time.format.*;
import java.time.temporal.ChronoUnit;
import java.awt.EventQueue;
import javax.swing.*;
import java.awt.*;
//import java.awt.BorderLayout;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
//import java.awt.geom.*;
import java.time.LocalDate;

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.Line2D;
//import java.awt.BasicStroke;
import javax.swing.JFrame;
//import javax.swing.SwingUtilities;


public class Test2GUI extends JFrame {

	public static JFrame frmBiorhythmus;
	public static JTextField textFieldD1;
	public static JTextField textFieldD2;
	public static JLabel lblNewLabelTage = new JLabel("");

	/**
	 * Launch the application.
	 */
	public static void main(String[] args) {
		EventQueue.invokeLater(new Runnable() {
			public void run() {
				try {
					Test2GUI window = new Test2GUI();
					window.frmBiorhythmus.setVisible(true);
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		});
	}

	/**
	 * Create the application.
	 */
	public Test2GUI() {
		initialize();
	}

	/**
	 * Initialize the contents of the frame.
	 */
	private void initialize() {
		frmBiorhythmus = new JFrame();
		frmBiorhythmus.addWindowListener(new WindowAdapter() {
			@Override
			public void windowActivated(WindowEvent e) {
				LocalDate d2 = LocalDate.now();
				DateTimeFormatter dFormat = DateTimeFormatter.ofPattern("dd.MM.yyyy");
				textFieldD2.setText(d2.format(dFormat));
			}
		});
		frmBiorhythmus.setResizable(false);
		frmBiorhythmus.setTitle("Biorhythmus");
		frmBiorhythmus.setBounds(100, 100, 516, 519);
		frmBiorhythmus.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frmBiorhythmus.getContentPane().setLayout(null);
		
		JLabel lblNewLabelD1 = new JLabel("Geburtsdatum:");
		lblNewLabelD1.setBounds(28, 28, 116, 14);
		frmBiorhythmus.getContentPane().add(lblNewLabelD1);
		
		JLabel lblNewLabelD2 = new JLabel("Berechnungsdatum:");
		lblNewLabelD2.setBounds(28, 64, 116, 14);
		frmBiorhythmus.getContentPane().add(lblNewLabelD2);
		
		textFieldD1 = new JTextField();
		textFieldD1.setText("15.05.1962");
		textFieldD1.setBounds(153, 25, 86, 20);
		frmBiorhythmus.getContentPane().add(textFieldD1);
		textFieldD1.setColumns(10);
		
		textFieldD2 = new JTextField();
		textFieldD2.setText("01.01.2022");
		textFieldD2.setBounds(154, 61, 86, 20);
		frmBiorhythmus.getContentPane().add(textFieldD2);
		textFieldD2.setColumns(10);
		
		JButton btnNewButtonOK = new JButton("berechnen");
		btnNewButtonOK.addMouseListener(new MouseAdapter() {
			@Override
			public void mouseClicked(MouseEvent e) {
				GetData();
			}
		});
		btnNewButtonOK.setBounds(285, 60, 105, 23);
		frmBiorhythmus.getContentPane().add(btnNewButtonOK);
		lblNewLabelTage.setVerticalAlignment(SwingConstants.TOP);
		
		lblNewLabelTage.setBounds(153, 136, 237, 116);
		frmBiorhythmus.getContentPane().add(lblNewLabelTage);
		
		centreWindow(frmBiorhythmus);
	}


	static void centreWindow(Window frame) {
		Dimension dimension = Toolkit.getDefaultToolkit().getScreenSize();
		int x = (int) ((dimension.getWidth() - frame.getWidth()) / 2);
		int y = (int) ((dimension.getHeight() - frame.getHeight()) / 2);
		frame.setLocation(x, y);
	}


	static void GetData() {
	   String d1s = textFieldD1.getText();
	   String d2s = textFieldD2.getText();
	   DateTimeFormatter df = DateTimeFormatter.ofPattern("dd.MM.yyyy");
	   LocalDate d1 = LocalDate.parse(d1s, df);
	   LocalDate d2 = LocalDate.parse(d2s, df);
	   // check dates
	   // ...

	   // calc
	   double d = ChronoUnit.DAYS.between(d1, d2);
	   int k = (int) (Math.sin((d / 23 - Math.rint(d / 23)) * Math.PI * 2) * 100);
	   int s = (int) (Math.sin((d / 28 - Math.rint(d / 28)) * Math.PI * 2) * 100);
	   int g = (int) (Math.sin((d / 33 - Math.rint(d / 33)) * Math.PI * 2) * 100);
	   String txt = "<html>";
	   txt += "Sie sind  " + (int) d + "  Tage alt.<br>";
	   txt += "körperlich: " + (k >= 0 ? "+" : "") + k + "%<br>";
	   txt += "seelisch: " + (s >= 0 ? "+" : "") + s + "%<br>";
	   txt += "geistig: " + (g >= 0 ? "+" : "") + g + "%<br>";
	   lblNewLabelTage.setText(txt);

	   // some basics
	   double x0 = frmBiorhythmus.getWidth() / 2;
	   double y0 = frmBiorhythmus.getHeight() - lblNewLabelTage.getAlignmentY() + lblNewLabelTage.getHeight() - 50;
	   double dx = frmBiorhythmus.getWidth() * 0.8 / 200;
	   double dy = (frmBiorhythmus.getHeight() - x0 - 20) / 10;
	   frmBiorhythmus.revalidate();
       frmBiorhythmus.repaint();
	}


	public void paint(Graphics g) {
		super.paint(g);
		Graphics2D g2 = (Graphics2D) g;
		Line2D lin = new Line2D.Float(0, 0, 2500, 2000);
		g2.draw(lin);
		JOptionPane.showMessageDialog(null, "#1", "Info", JOptionPane.INFORMATION_MESSAGE);
	}

	public void paintComponent(Graphics g){
        super.paintComponents(g);
        g.drawLine(0,20,100,20);
		JOptionPane.showMessageDialog(null, "#2", "Info", JOptionPane.INFORMATION_MESSAGE);
    }


}

What I have tried:

Some swing drawing examples from the net.