/**
 * CircleWindow shows how to create a simple window with a green
 * circle in it. Following CircleWindow, note the definition for the
 * class DrawingPanel, which is used in CircleWindow.
 *
 * @author Dave Musicant
 */

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

public class CircleWindow
{
    public static void main(String[] args)
    {
        // Instantiate a JFrame object, which is a generic "shell" for
        // holding graphics objects. Set size, location, and instruct
        // the jframe that it should cause your program to exit when
        // the jframe is closed.
        JFrame jframe = new JFrame("Drawing demo");
        jframe.setSize(250,300);
        jframe.setLocation(50,50);
        jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // Instantiate a DrawingPanel object, which is a subclass of
        // JPanel. It is on this drawingPanel object that we will do
        // our actual drawing (see the paintComponent method below).
        // Add the drawingPanel to the frame.
        DrawingPanel drawingPanel = new DrawingPanel();
        jframe.add(drawingPanel);

        // Finally, make the window appear.
        jframe.setVisible(true);
    }
}

/*
 * DrawingPanel is a subclass of JPanel, where the paintComponent
 * method is overridden with instructions on how to draw a circle. The
 * Java Virtual Machine calls this paintComponent method whenever a
 * DrawingPanel object needs to be repainted, such as when the panel
 * first appears or when it is brought in front of other windows.
 *
 * @author Dave Musicant
 */

class DrawingPanel extends JPanel
{
    public void paintComponent(Graphics g) {
        g.setColor(Color.green);
        g.fillOval(100,10,100,100);
    }
}