Problem with displaying objects in GUI

Question

I'm just going through a small book on Java programming and the goal is to press a button to show a shape (ie: circle) and then to press a button to hide that same shape.
My idea was to simply add it in but change the visibility to true and false. Now, I get it to show perfectly but I can't get it to hide (ie: setVisiblity to false) for some reason. The problem lies in the actionPerformed method of the CommandMain class. I'm at a loss as to why I can't simply change the visibility of the object to true and false.
I've include the relevant code below
Thanks for all your help in advance.
================= COMMANDMAIN.JAVA =================
public class CommandMain extends JFrame implements ActionListener
{     JButton circleButton = new JButton("Make Circle");
     JButton squareButton = new JButton("Make Square");
     JButton undoButton = new JButton("Undo Last");
     JButton exitButton = new JButton("Exit");
     private static Vector objectList = new Vector(); // Stores objects in order
JPanel container = new JPanel();
     Button newCircle;     // Used to add a Circle object to the vector     
     Button newSquare;
     Button newShape;
Button objectToHide;
// CONSTRUCTOR
// PURPOSE: Used to set up all the buttons on our Panel
     public CommandMain()
     {     setSize(400,400);
     setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          // Add interactive ability to buttons
          circleButton.addActionListener(this);
squareButton.addActionListener(this);
undoButton.addActionListener(this);
          exitButton.addActionListener(this);
          // Add them so we can see them on the panel
this.container.add(circleButton);
this.container.add(squareButton);
this.container.add(undoButton);
          this.container.add(exitButton);
setContentPane(container);
setVisible(true);
     // PURPOSE: Used to create an instance of itself so we can see the frame
public static void main(String args[]) throws IOException
{    CommandMain window = new CommandMain();     }
     // PURPOSE: Used to perform actions based on the button picked by the user
public void actionPerformed(ActionEvent picked)
{     Object choice = picked.getSource();
if(choice == circleButton)     // CIRCLE WAS SELECTED
{     newShape = new Button("Circle");          
               Button newCircle = newShape.getShape();
               this.container.add(newCircle);     // Add it to my container
               newShape.execute();
objectList.add(newShape);     // Add the object to my Vector
               setContentPane(container);
repaint();     // Redraw the GUI because it changed
else if(choice == undoButton) // UNDO WAS SELECTED
{     if(objectList.size() > 0)     // Check to ensure we don't overstep the boundaries
{     System.out.println("UNDO Pressed");
                    objectToHide = (Button)objectList.elementAt(objectList.size()-1);
                    objectToHide.hideShape(); // <-- NOT WORKING
                    objectList.removeElementAt(objectList.size()-1);
                    setContentPane(container);
                    repaint();
} // End if(objectList.size() > 0)
} // End undoButton
          else if(choice == exitButton) // EXIT WAS SELECTED
          {     System.out.println("Goodbye: Application exiting");
               dispose();
               System.exit(0);          
          else // No idea what button was selected
{         System.out.println("ERROR: Invalid option");     }
========================== BUTTON.JAVA ==================
import java.awt.*;
import javax.swing.*;
public class Button extends JPanel
{     String objectShape;
     Button()
     Button(String shape)
     {     this.objectShape = shape; }
     public void execute()
     {     setVisible(true);     }
     public void hideShape()
     {     System.out.println("hideShape called");
          super.setVisible(false);
     public Button getShape()
     {     if(this.objectShape.equals("Circle"))
          {     System.out.println("Making a circle");     
               Circle newCircle = new Circle();
               return newCircle;
          else if(this.objectShape.equals("Square"))
          {     System.out.println("Making a square");     
               Square newSquare = new Square();
               return newSquare;
          return null;

Answer 1

This will do the job, read and learn
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class CommandMain extends JFrame implements ActionListener
     Shape    shape;
     JPanel   pan          = new JPanel();
     JPanel   but          = new JPanel();
     JButton  circleButton = new JButton("Make Circle");
     JButton  squareButton = new JButton("Make Square");
     JButton  undoButton   = new JButton("Undo Last");
     JButton  exitButton   = new JButton("Exit");
public CommandMain()
     super();
     setBounds(6,6,700,400);     
     addWindowListener(new WindowAdapter()
    {     public void windowClosing(WindowEvent ev)
               dispose();     
               System.exit(0);
     pan.setBackground(Color.pink);
     getContentPane().add("Center",pan);
     but.add(circleButton);
     but.add(squareButton);
     but.add(undoButton);
     but.add(exitButton);
     circleButton.addActionListener(this);
     squareButton.addActionListener(this);
     undoButton.addActionListener(this);
     exitButton.addActionListener(this);
     getContentPane().add("South",but);
     setVisible(true);
public void actionPerformed(ActionEvent a)
     if (a.getSource() == circleButton)
          pan.add(new Shape("Circle"));
          pan.revalidate();
     if (a.getSource() == squareButton)
          pan.add(new Shape("Square"));
          pan.revalidate();
     if (a.getSource() == undoButton && pan.getComponentCount() > 0)
           pan.remove(pan.getComponentCount()-1);
          pan.revalidate();
          pan.repaint();
     if (a.getSource() == exitButton)
          dispose();     
          System.exit(0); 
public class Shape extends JComponent
     String shape;
public Shape(String shape)
     this.shape = shape;
     setPreferredSize(new Dimension(20,20));
public void paintComponent(Graphics g)
     super.paintComponent(g);
     if (shape.equals("Circle"))
          g.drawOval(0,0,getWidth()-1,getHeight()-1);
     if (shape.equals("Square"))
          g.drawRect(0,0,getWidth()-1,getHeight()-1);     
public static void main (String[] args)
     new CommandMain();  
}       Noah