DrawDemo

import javax.swing.*;

import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

public class DrawDemo extends JApplet{

    private int x;
    private int y;
    private int[] xPoints;
    private int[] yPoints;
    private Graphics g;

    public void init()
    {
        getContentPane().setBackground(Color.BLACK);
        setSize(500, 500);
        xPoints = new int[6];
        yPoints = new int[6];
        addMouseListener(new GMouseListener());

    }

    public void paint(Graphics g)
    {
        super.paint(g);
        g.setColor(Color.RED);
        g.fillPolygon(xPoints, yPoints, xPoints.length);
    }

    private class GMouseListener extends MouseAdapter
    {
        int count = 0;
        public void mousePressed(MouseEvent e)
        {
           System.out.println(e.getX() + ", " + e.getY());
            xPoints[count] = e.getX();
            yPoints[count] = e.getY();
            count++;

            if (count == 6)
                repaint();
        }

    }
}