Java program to find the nodes which are at the maximum distance in a Binary Tree

import java.util.ArrayList;  
  
public class MaxDistance {  
  
    //Represent a node of binary tree  
    public static class Node{  
        int data;  
        Node left;  
        Node right;  
  
        public Node(int data){  
            //Assign data to the new node, set left and right children to null  
            this.data = data;  
            this.left = null;  
            this.right = null;  
            }  
          }  
  
    //Represent the root of binary tree  
    public Node root;  
  
    int[] treeArray;  
    int index = 0;  
  
    public MaxDistance(){  
        root = null;  
    }  
  
    //calculateSize() will calculate size of tree  
    public int calculateSize(Node node)  
    {  
        int size = 0;  
        if (node == null)  
         return 0;  
        else {  
            size = calculateSize (node.left) + calculateSize (node.right) + 1;  
            return size;  
        }  
    }  
  
    //convertBTtoArray() will convert binary tree to its array representation  
    public void convertBTtoArray(Node node) {  
        //Check whether tree is empty  
        if(root == null){  
            System.out.println("Tree is empty");  
            return;  
        }  
        else {  
            if(node.left != null)  
                convertBTtoArray(node.left);  
            //Adds nodes of binary tree to treeArray  
            treeArray[index] = node.data;  
            index++;  
            if(node.right != null)  
                convertBTtoArray(node.right);  
            }  
    }  
  
    //getDistance() will find distance between root and a specific node  
    public int getDistance(Node temp, int n1) {  
        if (temp != null) {  
            int x = 0;  
            if ((temp.data == n1) || (x = getDistance(temp.left, n1)) > 0  
                    || (x = getDistance(temp.right, n1)) > 0) {  
                //x will store the count of number of edges between temp and node n1  
                return x + 1;  
            }  
            return 0;  
        }  
        return 0;  
    }  
  
    //lowestCommonAncestor() will find out the lowest common ancestor for nodes node1 and node2  
    public Node lowestCommonAncestor(Node temp, int node1, int node2) {  
        if (temp != null) {  
            //If root is equal to either of node node1 or node2, return root  
            if (temp.data == node1 || temp.data == node2) {  
                return temp;  
            }  
  
            //Traverse through left and right subtree  
            Node left = lowestCommonAncestor(temp.left, node1, node2);  
            Node right = lowestCommonAncestor(temp.right, node1, node2);  
  
            //If node temp has one node(node1 or node2) as left child and one node(node1 or node2) as right child  
            //Then, return node temp  as lowest common ancestor  
            if (left != null && right != null) {  
                return temp;  
            }  
  
            //If nodes node1 and node2 are in left subtree  
            if (left != null) {  
                return left;  
            }  
            //If nodes node1 and node2 are in right subtree  
            if (right != null) {  
                return right;  
            }  
        }  
        return null;  
    }  
  
    //findDistance() will find distance between two given nodes  
    public int findDistance(int node1, int node2) {  
        //Calculates distance of first node from root  
        int d1 = getDistance(root, node1) - 1;  
        //Calculates distance of second node from root  
        int d2 = getDistance(root, node2) - 1;  
  
        //Calculates lowest common ancestor of both the nodes  
        Node ancestor = lowestCommonAncestor(root, node1, node2);  
  
        //If lowest common ancestor is other than root then, subtract 2 * (distance of root to ancestor)  
        int d3 = getDistance(root, ancestor.data) - 1;  
        return (d1 + d2) - 2 * d3;  
    }  
  
    //nodesAtMaxDistance() will display the nodes which are at maximum distance  
    public void nodesAtMaxDistance(Node node) {  
        int maxDistance = 0, distance = 0;  
        ArrayList<Integer> arr = new ArrayList<>();  
  
        //Initialize treeArray  
        int treeSize = calculateSize(node);  
        treeArray = new int[treeSize];  
  
        //Convert binary tree to its array representation  
        convertBTtoArray(node);  
  
        //Calculates distance between all the nodes present in binary tree and stores maximum distance in variable maxDistance  
        for(int i = 0; i < treeArray.length; i++) {  
            for(int j = i; j < treeArray.length; j++) {  
                distance = findDistance(treeArray[i], treeArray[j]);  
                //If distance is greater than maxDistance then, maxDistance will hold the value of distance  
                if(distance > maxDistance) {  
                    maxDistance = distance;  
                    arr.clear();  
                    //Add nodes at position i and j to treeArray  
                    arr.add(treeArray[i]);  
                    arr.add(treeArray[j]);  
                }  
                //If more than one pair of nodes are at maxDistance then, add all pairs to treeArray  
                else if(distance == maxDistance) {  
                    arr.add(treeArray[i]);  
                    arr.add(treeArray[j]);  
                }  
            }  
        }  
        //Display all pair of nodes which are at maximum distance  
        System.out.println("Nodes which are at maximum distance: ");  
        for(int i = 0; i < arr.size(); i = i + 2) {  
            System.out.println("( " + arr.get(i) + "," + arr.get(i+1) + " )");  
        }  
    }  
  
    public static void main(String[] args) {  
  
        MaxDistance bt = new MaxDistance();  
        //Add nodes to the binary tree  
        bt.root = new Node(1);  
        bt.root.left = new Node(2);  
        bt.root.right = new Node(3);  
        bt.root.left.left = new Node(4);  
        bt.root.left.right = new Node(5);  
        bt.root.right.left = new Node(6);  
        bt.root.right.right = new Node(7);  
        bt.root.right.right.right = new Node(8);  
        bt.root.right.right.right.left = new Node(9);  
  
        //Finds out all the pair of nodes which are at maximum distance  
        bt.nodesAtMaxDistance(bt.root);  
      }  
}  

Output:

Nodes which are at maximum distance: 
( 4, 9 )
( 5, 9 )