Problem with invoking an Action in a Menu...

Question

I wanted to make a program that would create a box of rectangles and have each rectangle change color when clicked.
I want the user to be able to decide which color you want the rectangle to be. I put choices in a menu.
However whenever an option is selected from the menu, I get exceptions:
Exception occurred during event dispatching:
java.lang.NullPointerException
at ShapeTest$ColorAction$ColorThread.run(ShapeTest.java:142)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:154)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:337)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:131)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:98)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:85)
The code is displayed below. Am I missing something with the Swing thread? Please help.
Josh
import javax.swing.*;
import java.awt.*;
import java.awt.geom.*;
import java.awt.event.*;
// This Rectangle knows it's particular color
class ColorRectangle extends Rectangle2D.Float
   private Color color;
   public ColorRectangle( float x, float y, float w, float h, Color c )
      super( x, y, w, h );
      color = c;
   public ColorRectangle( float x, float y, float w, float h)
      super( x, y, w, h );
      color = Color.white;
   public void setColor( Color c )
      color = c;
   public Color getColor()
      return color;
} // end ColorRectangle class
   This is the main frame.
public class ShapeTest extends JFrame
   private ShapeTestPanel panel;
   public ShapeTest()
      setTitle( "ShapeTest" );
      setSize( 500, 500 );
      setDefaultCloseOperation( EXIT_ON_CLOSE );
      JPanel panel = new ShapeTestPanel();
      Container cp = getContentPane();
      cp.add( panel, BorderLayout.CENTER );
      // Set up the menu
      JMenuBar mb = new JMenuBar();
      JMenu mColor = new JMenu( "Color" );
      mColor.setMnemonic( KeyEvent.VK_C );
      // Adding the actions to the menu
      mColor.add( new ColorAction("Blue", Color.blue, KeyEvent.VK_B) );
      mColor.add( new ColorAction("Green", Color.green, KeyEvent.VK_G) );
      mColor.add( new ColorAction("Red", Color.red, KeyEvent.VK_R) );
      mColor.add( new ColorAction("White", Color.white, KeyEvent.VK_W) );
      mb.add( mColor );
      setJMenuBar( mb );
   } // end ShapeTest constructor
   public static void main( String [] args )
      JFrame frame = new ShapeTest();
      frame.setVisible( true );
      This action inner class will be added to the menu to change the main color
      of the panel.
   class ColorAction extends AbstractAction
      private Color color;
      private ColorThread thread; // this is used to change panel color
      public ColorAction( String name, Color c, int keyEvent )
         putValue( NAME, name );
         putValue( MNEMONIC_KEY, new Integer(keyEvent) );
         color = c;
         thread = new ColorThread();
         Here I want to change the main color of the panel, so that
            clicking on a rectangle will now display a different color.
      public void actionPerformed( ActionEvent evt )
            I tried to just call the function panel.setMainColor( color ).
            EXCEPTION!!!
            I tried to make the mainColor variable public and access it.
            EXCEPTION!!!
            I tried to use SwingUtilities.invokeLater( thread ).
            EXCEPTION!!!
            I tried to use SwingUtilities.invokeAndWait( thread );
            EXCEPTION!!!
         try
            SwingUtilities.invokeLater( thread );
         catch ( Exception ex )
            System.out.println( ex );
      } // end actionPerformed( evt )
      // Inner class of an inner class
      class ColorThread extends Thread
         public void run()
            panel.setMainColor( color );
            // panel is a member of the frame.
      } // end ColorThread class
   } // end ColorAction class
} // end ShapeTest class
class ShapeTestPanel extends JPanel
   private Rectangle2D bigRect; // the outer rectangle
   private ColorRectangle [][] araRects; // the inner rectangles
   public Color mainColor = Color.blue; // will change inner rectangle
                                        //   color on mouseClicked
   public ShapeTestPanel()
      int x = 10;
      int y = 10;
      // Make the outer rectangle
      bigRect = new Rectangle2D.Double( x, y, 401, 401 );
      // Make the inner rectangles
      araRects = new ColorRectangle [4][4];
      int i, j;
      for ( x = 11, i = 0; i < araRects.length; i++, x += 100 )
         for ( y = 11, j = 0; j < araRects.length; j++, y += 100 )
araRects[i][j] = new ColorRectangle( x, y, 99, 99 );
addMouseListener( new ShapeTestMouseListener() );
} // end ShapeTestPanel constructor
// This will change the main color for clicking
public void setMainColor( Color c )
mainColor = c;
// Draw the outer rectangle and the inner rectangles in the right color
public void paintComponent( Graphics g )
super.paintComponent( g );
Graphics2D g2 = (Graphics2D)g;
g2.draw( bigRect );
for ( int i = araRects.length - 1; i > -1; i-- )
for ( int j = araRects[i].length - 1; j > -1; j-- )
g2.setPaint( Color.black );
g2.draw( araRects[i][j] );
g2.setPaint( araRects[i][j].getColor() );
g2.fill( araRects[i][j] );
} // end paintComponent( Graphics g )
// I want the color to change when someone clicks on a rectangle
class ShapeTestMouseListener extends MouseAdapter
public void mouseClicked( MouseEvent evt )
Point p = evt.getPoint();
for ( int i = araRects.length - 1; i > -1; i-- )
for ( int j = araRects[i].length - 1; j > -1; j-- )
if ( araRects[i][j].contains(p) )
araRects[i][j].setColor( mainColor );
repaint();
return;
} // mouseClicked( MouseEvent )
} // end ShapeTestMouseListener class
} // end ShapeTestPanel

Answer 1

replace the following line
JPanel panel = new ShapeTestPanel();
with
this.panel = new ShapeTestPanel(); in the ShpaeTest constructor