10.5 Depth First Traversing

http://blog.csdn.net/benweizhu/article/details/7930697

http://www.gocalf.com/blog/traversing-binary-tree.html

  public void inOrder(Node current) {  
        if (current != null) {  
            inOrder(current.left);  
            System.out.print(current.value);  
            inOrder(current.right);  
        }  
    }  

  public void preOrder(Node current) {  
        if (current != null) {  
            System.out.print(current.value);  
            preOrder(current.left);  
            preOrder(current.right);  
        }  
    }

  public void postOrder(Node current) {  
        if (current != null) {  
            postOrder(current.left);  
            postOrder(current.right);  
            System.out.print(current.value);  
        }  
    }