import java.awt.*;
import java.awt.geom.*;
import javax.swing.*;

public class Canvas extends JPanel {
    // This is the draw callback
    public void paintComponent (Graphics g) { //*1 Right way, draw in the callback
	super.paintComponent(g); //*3 Supposed to chain to superclass, which clears background first
	g.drawLine (50, 50, 100, 50); //*2 Draw on the "g" object
    }
}