how to draw a line in java

1import javax.swing.*;
2import java.awt.*;
3
4class Scratch extends JComponent{
5    public static void main(String[] args) {
6        JFrame window = new JFrame();   // creates a JFrame
7        window.setTitle("Example");     //sets the title
8        window.setSize(600, 600);   //sets the size
9        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  // sets the default close operation
10        window.setVisible(true);    //sets the JFrame visible
11        Scratch drawing = new Scratch();    //indirectly calls the paint method
12        window.add(drawing);    //adds the paint method onto the JFrame
13    }
14
15    public void paint(Graphics g){
16        Graphics2D g2 = (Graphics2D) g; //casting
17        g2.drawLine(100, 200, 300, 400);    //Draws a line from (100, -200) -> (300, -400) on the x and y plane
18        g2.draw(new Rectangle(10, 10, 10, 10));     //draw a rectangle
19        g2.setColor(Color.GREEN);   //Changes colour to Green
20        g2.fill(new Rectangle(100, 100, 100, 100)); //fills a rectangle
21    }
22}