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

// the gameworld is a component, so it can be added to a GUI program
class Canvas extends JComponent {
    @Override
    // overriding this method changes how it is shown
    public void paintComponent(Graphics g) {
        // just draw a black line on the window
        g.setColor(Color.green);
        g.fillOval(200, 200, 100, 100);
    }
}

public class SimpleGraphics {
    public static void main(String args[]) {
        // create and set up the window.
        JFrame frame = new JFrame("Graphics Example!");

        // make the program close when the window closes
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // add the GameWorld component
        frame.add(new Canvas());

        // display the window.
        frame.setSize(500, 500);
        frame.setVisible(true);
    }
}