JTree: What do I do, when a leaf node isn't a leaf node?

Question

Hi All,
I have a question about the JTree and leaf nodes.
My requirements are:
1) I have to have a tree which doesn't "fill" its contents at a certain level until the user expands a node
2) As a result of #1, leaf nodes must have a "+" sign in front of them until the user tries to expand them at least once (if they are then empty, the "+" is removed in favor of the normal leaf icon.. if they have data, the "+" is replaced with a "-" and the data is filled in)..
Currently, we have an implementation of this which adds a "dummy" node as a child of the leaf to force it to be a "non-leaf", until the user opens it, then the dummy object is removed and the real data (if any) is added..
It works, but I'm wondering if there is a simpler way.
Can anyone offer their opinion? Thanks a bunch.
Dave

Answer 1

What I do is to have some code that implements TreeWillExpandListener. What happens then is that when the user clicks on the doohickey to expand a node, my treeWillExpand(TreeExpansionEvent e) method is called. It examines the node that is about to expand and goes out to the database to load up its children. But to make this work, you have to have the doohickey available. This means that your nodes have to know whether their children have been loaded or not; this is the code I use to override the isLeaf() method for them:public boolean isLeaf() {
  return (childrenLoaded ? super.isLeaf() : false);
}In this code "childrenLoaded" is a boolean instance variable that is initialized to false, then set to true via a property-setter method by the code that loads the node's children.
That's a rough outline of what I did. Good luck!