Implementation for the method: Findpathbetween The node class:  

public class BSTNode> { private T data; private BSTNode left; private BSTNode right; /**  * Create a BST node with the given data.  *  * @param data the data to be stored in this node.  */  public BSTNode(T data) { this.data = data; } /**  * Get the data in this node.  *  * @return data in this node.  */  public T getData() { return data; } /**  * Set the data in this node.  *  * @param data data to be placed into the node.  */  public void setData(T data) { this.data = data; } /**  * Get the node to the left of this node.  *  * @return node to the left.  */  public BSTNode getLeft() { return left; } /**  * Set the node to the left of this node.  *  * @param left new node to the left.  */  public void setLeft(BSTNode left) { this.left = left; } /**  * Get the node to the right of this node.  *  * @return node to the right.  */  public BSTNode getRight() { return right; } /**  * Set the node to the right of this node.  *  * @param right new node to the right.  */  public void setRight(BSTNode right) { this.right = right; } } 

The interface for the method: /** * Finds a path between two elements in the tree, specifically the path  * from data1 to data2, inclusive of both.  *  * To do this, you must first find the deepest common ancestor and add it  * to the list, then traverse to data1 while adding its ancestors to the  * front of the list then traverse to data2 while adding its ancestors to  * the back of the list. Please note that there is no relationship  * between the data parameters in that they may not belong to the same  * branch. You will most likely have to split off and traverse the tree  * for each piece of data.  *  * You may only use 1 list instance to complete this method. This method  * should only need to traverse to the deepest common ancestor once, and  * from that node to each data in one traversal each. Failure to  * do so will result in a penalty.  *  * Should run in O(n).  *  * @param data1 The data to start the path from  * @param data2 The data to end the path on  * @return the unique path between two elements  * @throws IllegalArgumentException if either data1 or data2 is null  * @throws java.util.NoSuchElementException if data1 or data2 is not in  * the tree  */ List findPathBetween(T data1, T data2); 

I'm supposed to implement the method from the BST class :

import java.util.Collection; import java.util.List; 

public class BST> implements BSTInterface { // DO NOT ADD OR MODIFY INSTANCE VARIABLES. private BSTNode root; private int size; /**  * A no argument constructor that should initialize an empty BST.  * YOU DO NOT NEED TO IMPLEMENT THIS CONSTRUCTOR!  */  public BST() { } /**  * Initializes the BST with the data in the Collection. The data in the BST  * should be added in the same order it is in the Collection.  *  * @param data the data to add to the tree  * @throws IllegalArgumentException if data or any element in data is null  */  public BST(Collection data) { if (data == null) { throw new IllegalArgumentException(""); } for (T item : data) { add(item); } } 

@Override public List findPathBetween(T data1, T data2) { if (data1 == null || data2 == null) { throw new IllegalArgumentException(""); } // }