Java Swing How to - Paint on/with JScrollPane

Question

We would like to know how to paint on/with JScrollPane.
Answer

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
//from  w  ww  . j  a  v a  2 s.  c  om
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;

public class Main{
  public static void main(String[] args) {
    java.awt.EventQueue.invokeLater(new Runnable() {
      public void run() {
        JScrollPane scrollpane = new JScrollPane(new ScrollPaneArtifacts());
        scrollpane.getViewport().setPreferredSize(new Dimension(400, 400));
        JFrame frame = new JFrame("ScrollPaneArtifacts");
        frame.getContentPane().add(scrollpane);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
      }
    });
  }
} 

class ScrollPaneArtifacts extends JPanel {
  private static final int SPA_WIDTH = 600;
  private static final int SPA_HEIGHT = SPA_WIDTH;

  @Override
  protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    g.setColor(Color.red);
    g.drawLine(0, 0, getWidth(), getHeight());
    g.drawLine(getWidth(), 0, 0, getHeight());
  }

  @Override
  public Dimension getPreferredSize() {
    return new Dimension(SPA_WIDTH, SPA_HEIGHT);
  }
}