Given the following IntTree class, I am wondering if the implementations of the preorder, postorder and level order methods are correct, and if not what should be changed in them.

Would like to keep the 3 constructors the same if possible.

import java.io.*;

import java.util.*;

public class IntTree {

private class Node {

private int data;

private Node firstChild;

private Node sibling;

private Node parent;

private Node (int d, Node f, Node s, Node p) {

data = d;

firstChild = f;

sibling = s;

parent = p;

}

}

private Node root;

public IntTree(int d) {

//create a one node tree

root = addNode(root, d);

}

public IntTree(IntTree t[], int d) {

//create a new tree whose children are the trees in t and whose root value is d

Node newTree = new Node(d, t[d].root.firstChild, t[d].root.sibling, t[d].root.parent);

}

public IntTree(int d[]) {

//create a tree with d[0] as the root value and the other values as children of the root

for(int i = 0; i < d.length; i++) {

addNode(root, d[i]);

}

}

private Node addNode(Node currNode, int value) {

//Add a Node to the tree

if(currNode == null) {

return new Node(value, root, null, null);

}

if(value < currNode.data) {

currNode.firstChild = addNode(currNode.firstChild, value);

}

else if(value > currNode.data) {

currNode.sibling = addNode(currNode.sibling, value);

}

else {

return currNode;

}

return currNode;

}

public String preorder() {

//return a string of the ints in the tree in preorder

//separate the ints with commas

//the implementation must be recursive

return preOrder(root);

}

private String preOrder(Node r) {

String s = "";

if(r != null) {

preOrder(r.parent);

preOrder(r.firstChild);

preOrder(r.sibling);

s = r.data + "" + ",";

}

return s;

}

public String postorder() {

//return a string of the ints in the tree in postorder

//separate the ints with commas

//the implementation must be recursive

return postOrder(root);

}

private String postOrder(Node r) {

String s = "";

if(r != null) {

postOrder(r.firstChild);

postOrder(r.sibling);

postOrder(r.parent);

s = r.data + "" + ",";

}

return s;

}

public String levelorder() {

//return a string of the ints in the tree in level order (also know a breadth first order)

//separate the ints with commas

//the implementation must be iterative

return printLevelOrder();

}

private String printLevelOrder() {

LinkedList nodeList = new LinkedList<>();

nodeList.add(root);

String s = "";

while(nodeList.size() > 0) {

Node r = nodeList.remove();

if(r.parent != null) {

nodeList.add(r.parent);

}

if(r.firstChild != null) {

nodeList.add(r.firstChild);

}

if(r.sibling != null) {

nodeList.add(r.sibling);

}

s = r.data + "" + ",";

}

return s;

}

}

Thanks for your help!