import javax.swing.*;
import java.util.*;
import java.awt.Polygon;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Rectangle;

public class PolygonCanvas
    extends JPanel
{
    private int    width;
    private int    height;
    private Vector polygons = new Vector();
    
    PolygonCanvas( int w, int h )
    {
        width = w;
        height = h;
        setPreferredSize( new Dimension( w, h ));
    }
    
    public void paintComponent( Graphics g )
    {
        super.paintComponent( g );
        int n = polygons.size();
        
        for ( int i = 0; i < n; i++ )
        {
            Polygon p = (Polygon) polygons.elementAt( i );
            
            g.drawPolygon( p );
        }
    }
    
    public void addPolygon( Polygon p )
    {
        polygons.addElement( p );
        
        Rectangle r = p.getBounds();
        repaint( r.x, r.y, r.width, r.height );
    }
}