Hiding / Filtering nodes in a JTree

Question

I'm not exactly sure how to temporarily hide or filter nodes from a JTree. My scenario is described below.
I have a radio button group. If the first radio button is selected, all nodes are displayed. If the second button is selected, certain nodes are hidden.
Here is my attempt to filter nodes. I get the following excpetion when I try to filter nodes:
java.lang.NullPointerException: Null child not allowed
I assume this is coming from the getChild() method. I don't know what else to return besides null if I'm trying to filter the node out.
Can anyone provide some help or insight?
Thanks
import javax.swing.tree.DefaultTreeModel;
import javax.swing.tree.DefaultMutableTreeNode;
public class MyTreeModel extends DefaultTreeModel
    * Constructor.
    * @param rootNode The root node.
   public MyTreeModel( DefaultMutableTreeNode rootNode )
      super( rootNode );
    * Gets the child node.
    * @param parent The parent node.
    * @param index The index this child node resides in.
    * @return The child node.
   public Object getChild( Object parent, int index )
      Object child = super.getChild( parent, index );
      if ( RadioBtn.hideNodes() )
         DefaultMutableTreeNode dmtn = ( DefaultMutableTreeNode ) child;
         MyNode eNode = ( MyNode ) dmtn.getUserObject();
         if ( !eNode.hasPermission() )
            child = null;    // "hide" the node
      return child;
    * Gets the index of a child.
    * @param parent The parent node.
    * @param child The child node.
    * @return The index of the child node.
    public int getIndexOfChild( Object parent, Object child )
       int index = super.getIndexOfChild( parent, child );
       if ( RadioBtn.hideNodes() )
          DefaultMutableTreeNode dmtn = ( DefaultMutableTreeNode ) parent;
          MyNode eNode = ( MyNode ) dmtn.getUserObject();
          if ( !eNode.hasPermission() )
             index = -1;
       return index;
    * Returns the number of children attached to the parent node.
    * @param parent The parent node.
    * @return The number of children of the parent node.
   public int getChildCount( Object parent )
      int numChildren = super.getChildCount( parent );
      if ( RadioBtn.hideNodes() )
         int counter = 0;
         DefaultMutableTreeNode dmtn = ( DefaultMutableTreeNode ) parent;
         // Loop through children and keep a count of all children nodes that should stay
         for ( int x = 0; x < numChildren; x++ )
            DefaultMutableTreeNode childDmtn = ( DefaultMutableTreeNode ) dmtn.getChildAt( x );
            MyNode eNode = ( MyNode ) childDmtn.getUserObject();
            if ( eNode.hasPermission() )
               counter++;
         numChildren = counter;
      System.out.println( "Number of children in " + ( DefaultMutableTreeNode ) parent + ": " + numChildren );
      return numChildren;
    * Used from radio buttons to toggle hidden folders on and off.
   public void triggerMe()
      reload();

Answer 1

Here it is optimized, for anyone who may need the code down the road.
   public Object getChild( Object parent, int index )
      Object child = super.getChild( parent, index );
      if ( RadioBtn.isHidden() ) // If we should remove the 'special' nodes
         DefaultMutableTreeNode dParent = ( DefaultMutableTreeNode ) parent;
         int count = 0;
         // Loop through children
         for ( int x = 0; x < dParent.getChildCount(); x++ )
            DefaultMutableTreeNode dChild = ( DefaultMutableTreeNode ) dParent.getChildAt( x );
            MyNode eNode = ( MyNode ) dChild.getUserObject();
            if ( eNode.hasPermission() )
               // If it is the "xth" visible node, break the loop and set this object as the Child node
               if ( count == index )
                  child = dChild;
                  break;
               count++;
      return child;
   }