IceUserObject - the Object that constitutes a DefaultMutableTreeNode's
user-specified data.
The TreeModel must contain a tree of DefaultMutableTreeNode instances. Each
DefaultMutableTreeNode instance encapsultes an IceUserObject. The
IceUserObject is the extension point for the application developer.
By default all nodes are folders unless the leaf attribute is set true.
If the IceUserObject does not provide sufficient state for representation of
the tree's nodes, then the application developer should extend the
IceUserObject and add state as required to their extension. When creating an
IceUserObject, the DefaultMutableTreeNode wrapper must be provided to the
constructor. Then the node's state can be set to the attributes on the
IceUserObject.
Set the value of the boolean leaf attribute. Setting the leaf
attribute to true will force a tree node to be rendered as a leaf. By
default the leaf attribute is false therefore all tree nodes will default
to folders.