import java.awt.*;

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

public class PaintClass {

    public PaintClass() {
        JFrame frame = new JFrame("Linie zeichnen") {
            public void paint(Graphics g) {
                g.drawLine(50, 50, 200, 200);
            }
        };
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(400, 400);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

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