1 public class BinaryTree 
 2 {
 3     Node root, head;
 4       
 5     // Initialize previously visited node as NULL. This is
 6     // static so that the same value is accessible in all recursive
 7     // calls
 8     Node prev = null;
 9   
10     // A simple recursive function to convert a given Binary tree 
11     // to Doubly Linked List
12     // root --> Root of Binary Tree
13     void BinaryTree2DoubleLinkedList(Node root) {
14         // Base case
15         if (root == null) return;
16   
17         // Recursively convert left subtree
18         BinaryTree2DoubleLinkedList(root.left);
19   
20         // Now convert this node
21         if (prev == null){
22             head = root;
23         } else {
24             root.left = prev;
25             prev.right = root;
26         }
27         prev = root;
28   
29         // Finally convert right subtree
30         BinaryTree2DoubleLinkedList(root.right);
31     }
32     
33     void printList(Node node)
34     {
35         while (node != null) 
36         {
37             System.out.print(node.data + " ");
38             node = node.right;
39         }
40     }
41   
42     // Driver program to test above functions
43     public static void main(String[] args) 
44     {
45         // Let us create the tree as shown in above diagram
46         BinaryTree tree = new BinaryTree();
47         tree.root = new Node(10);
48         tree.root.left = new Node(12);
49         tree.root.right = new Node(15);
50         tree.root.left.left = new Node(25);
51         tree.root.left.right = new Node(30);
52         tree.root.right.left = new Node(36);
53   
54         // convert to DLL
55         tree.BinaryTree2DoubleLinkedList(tree.root);
56           
57         // Print the converted List
58         tree.printList(tree.head);
59   
60     }
61 }
62 
63 
64 class Node 
65 {
66     int data;
67     Node left, right;
68   
69     public Node(int data) 
70     {
71         this.data =http://www.mamicode.com/ data;
72         left = right = null;
73     }
74 }