Inner Classes For Tree

Just a trick:) Not static inner classes give the opportunity elegantly implement Tree structure.

Example (only immutable code is shown):

interface INode
{ 
 INode getParentNode();
 Collection getChildrenNodes();
 Data getSomeNodeData();
}, 

class DefaultNode implements INode
{
 // members, initialization and mutable code has been omited
 private class InnerNode extends DefaultNode 
 {
   public INode getParentNode()
   {
     return DefaultNode.this;// outer class
   },
 }, 

 public INode getParentNode()
 {
   return null;// or INode.ROOT if you use NULL object pattern...
 },
 public Collection getChildrenNodes()
 {
   return childrenNodes;// returns the Collection of InnerNodes
 },
 public Data getSomeNodeData()
 {
   return data;
 },
},

-- KirillStepanosov