Swing Help

[Metsfan147]

Hi there. I'm trying to write some code to display a graph with nodes/edges on a LayeredPane that will allow the user to move the nodes around. However, I am having some problems getting my nodes to show up. Whenever I launch the application, I just get a blank window. Does anyone have any ideas? Attached is the relevant file.

class GraphGUI extends JPanel
{    
    /**The frame that everything will lie in.*/
    private JFrame mainFrame;

    /**The panel that the nodes will lay in.*/
    private JPanel nodesPanel;

    /**LayeredPane to implement moving of the
     * nodes within the windows.*/
    private JLayeredPane nodeLayer;

    /**The default size of the main panel.*/
    private Dimension DEFAULT_DIMENSION = new Dimension( 650, 500 );

    /**The graph object currently associated with the application.*/
    private MatrixGraph graph;

    /**The labels that will represent nodes of the graph.*/
    private JLabel[] nodeLabels;

    /**The default background color of the nodes*/
    private Color nodeBgColor = Color.ORANGE;

    /**
     * Default constructor, creates an empty window/frame.
     */
    public GraphGUI()
    {
        this.createMainComponents();
        graph = new MatrixGraph( 5 );
        this.createNodes();
        this.displayNodes();
        mainFrame.pack();
        mainFrame.setVisible( true );
    }

    /**Method to create the main frame components.  This includes the main frame
     * itself, the main panel that resides inside the pane, and the layered pane
     * for eventual drag and drop features.  This will also create the buttons panel
     * and the information panel that exists on the bottom.
     */
    private void createMainComponents( )
    {

        mainFrame = new JFrame( "Graph: name=?" );
        mainFrame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        mainFrame.setDefaultLookAndFeelDecorated( true );
        mainFrame.setLocationRelativeTo( null );
        mainFrame.setResizable( false );
        mainFrame.getContentPane().setLayout( new BorderLayout() );


        nodeLayer = new JLayeredPane();
        nodeLayer.setPreferredSize( DEFAULT_DIMENSION );

        nodesPanel = new JPanel();
        nodesPanel.add( nodeLayer );
        mainFrame.add( nodesPanel );

    }


    /**Creates all of the JLabels that will represent the nodes of the graph.
     */
    private void createNodes( )
    {
        if( this.graph == null )
        {
            System.err.println( "error!" );
        }

        this.nodeLabels = new JLabel[ graph.getSize() ];

        for( int i = 0; i < nodeLabels.length; ++i )
        {
            JLabel l = new JLabel( new Integer( i ).toString() );
            l.setOpaque( true );
            nodeLabels[ i ] = l;
        }
    }


    /**Puts the nodes on the screen in two rows.
     */
    private void displayNodes( )
    {

        for( int i = 0; i < nodeLabels.length; ++i )
        {
            nodeLayer.add( nodeLabels[i], JLayeredPane.DEFAULT_LAYER );
        }

    }
        



    public static void main( String[] args )
    {
        String LandFError = "Error setting the L&F, using default\n";
        try
        {
            UIManager.setLookAndFeel( UIManager.getSystemLookAndFeelClassName() );
            GraphGUI g = new GraphGUI();
        }

        catch ( ClassNotFoundException e )
        {
            System.err.println( LandFError );
        }
        
        catch( InstantiationException e )
        {
            System.err.println(  LandFError );
        }

        catch( IllegalAccessException e )
        {
            System.err.println(  LandFError );
        }

        catch( UnsupportedLookAndFeelException e )
        {
            System.err.println(  LandFError );
        }
    }
}