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