please use code in question to build answer

as well ad the postorder part below

apology for the very long question

Problem #3: (30 points In this problem, you will write some Java code for simple operations on binary search trees where keys are integers. Assume you already have the following code and assume that the method bodies, even though not shown, are correct and implement the operations as we defined them in class public class BinarySearchTreeNode public int key; public BinarySearchTreeNode left; public BinarySearchTreeNode right; public class BinarySearchTree private BinarySearchTreeNode root public void insert (int key) { 1 public void delete (int key) > public boolean find(int key) f... J (a) Add a method public int keySum() to the BinarySearch Iree class that returns the sum of all the keys in the tree. You will need an assistant/helper method (b) Add method public void deleteMin() to the Binary Search Tree class that deletes the minimum element in the tree (or does nothing if the tree has no elements) (c) Add method public void printTree() to the BinarySearch Tree class that iterates over the nodes to print then in increasing order. So the tree... 4 Produces the output "1 2 3 4 5