Perfeito Vini!!! 
Baseado no código daquele site que mensionei acima + suas dicas consegui fazer o que desejava…
Ao clicar em qualquer parte do primeiro retângulo com o direito do mouse o menu de contexto é aberto.
Segue o código à quem possa interessar:
[code]import javax.swing.*;
import java.awt.;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.geom.;
public class Rectangle2D1 extends JApplet implements ActionListener, ItemListener{
private Rectangle2D Shape1;
private Rectangle2D Shape2;
private Rectangle2D Shape3;
private Rectangle2D Shape4;
private boolean Contained;
public Rectangle2D1 () {
Shape1 = new Rectangle2D.Double ();
Shape1.setRect (20., 20., 100., 50.);
Shape2 = new Rectangle2D.Double (140., 20., 100., 50.);
Shape3 = new Rectangle2D.Float ();
Shape3.setRect (260., 20., 100., 50.);
Shape4 = new Rectangle2D.Float (380.F, 20.F, 100.F, 50.F);
createPopupMenu();
}
public void paint (Graphics g) {
Graphics2D g2D;
g2D = (Graphics2D) g;
g2D.draw (Shape1);
Contained = Shape1.contains (30., 30.);
g2D.drawString ("contains = " + Contained, 20, 90);
g2D.fill (Shape2);
Contained = Shape2.contains (160., 10., 30., 40.);
g2D.drawString ("contains = " + Contained, 140, 90);
g2D.draw (Shape3);
Contained = Shape3.intersects (280., 10., 30., 50.);
g2D.drawString ("intersects = " + Contained, 260, 90);
g2D.fill (Shape4);
Contained = Shape4.intersectsLine (400., 10., 490., 70.);
g2D.drawString ("intersectsLine = " + Contained, 380, 90);
g2D.setColor (Color.blue);
g2D.drawLine (10, 10, 10, 10);
g2D.drawLine (30, 30 - 10, 30, 30 + 10);
g2D.drawRect (160, 10, 30, 40);
g2D.drawRect (280, 10, 30, 50);
g2D.drawLine (400, 10, 490, 70);
}
public void createPopupMenu() {
JMenuItem menuItem;
//Create the popup menu.
JPopupMenu popup = new JPopupMenu();
menuItem = new JMenuItem("primeiro item do menu");
menuItem.addActionListener(this);
popup.add(menuItem);
menuItem = new JMenuItem("segundo item do menu");
menuItem.addActionListener(this);
popup.add(menuItem);
//Add listener to the area so the popup menu can come up.
MouseListener popupListener = new PopupListener(popup);
this.addMouseListener(popupListener);
}
class PopupListener extends MouseAdapter {
JPopupMenu popup;
PopupListener(JPopupMenu popupMenu) {
popup = popupMenu;
}
public void mousePressed(MouseEvent e) {
if(Contained = Shape1.contains(e.getX(), e.getY()))
{
maybeShowPopup(e);
}
}
public void mouseReleased(MouseEvent e) {
if(Contained = Shape1.contains(e.getX(), e.getY()))
{
maybeShowPopup(e);
}
}
private void maybeShowPopup(MouseEvent e) {
if (e.isPopupTrigger()) {
popup.show(e.getComponent(),e.getX(), e.getY());
}
}
}
@Override
public void actionPerformed(ActionEvent arg0) {
// TODO Auto-generated method stub
}
@Override
public void itemStateChanged(ItemEvent arg0) {
// TODO Auto-generated method stub
}
}[/code]
Mais uma vez, muito grato! 8)