Im new to generics and i have to implement a binary search tree using generics. I did that but now im wondering how do i test the code that i wrote? Do i just make another class and start using the methods of the bst?
any help would be appreciated. below is my code just to clarify.
public class BST<E extends Comparable<E>>
{
public Node<E> root;
public BST()
{
root = null;
}
//insert delete find height
public void find(E s, Node<E> n)
{
//empty tree, root is null
if(n == null)
{
System.out.println("Item not present.");
}
//n is the node where s is, return n
else if(n.getData().equals(s))
{
System.out.println("Item present");
}
//s is greater than n, look for s on the right subtree
else if(s.compareTo(n.getData()) > 0)
{
find(s, n.getRight());
}
//s is less than n, look for s on the left subtree
else
{
find(s, n.getLeft());
}
}
public int height()
{
int count;
return count = height(root);
}
private int height(Node<E> n)
{
int ct = 0;
if(n == null)
{
}
else
{
int left = height(n.getLeft());
int right = height(n.getRight());
ct = Math.max(left, right) + 1;
}
return ct;
}
public void insert(E s)
{
root = insert(s, root);
}
private Node<E> insert(E s, Node<E> T)
{
//easiest case, empty tree, create new tree
if(T == null)
{
T = new Node<E>(s,null,null);
}
//easiest case, found s
else if(s.compareTo(T.getData()) == 0)
{
System.out.println("Item already present.");
}
//s is greater than T, insert on right subtree
else if(s.compareTo(T.getData()) > 0)
{
T.setRight(insert(s, T.getRight()));
}
//s is less than T, insert on left subtree
else
{
T.setLeft(insert(s,T.getLeft()));
}
return T;
}
public void delete(E d)
{
}
}
and my node class
public class Node<E>
{
private E data;
private Node<E> left;
private Node<E> right;
private Node<E> parent;
public Node(E d, Node<E> r, Node<E> l)
{
data = d;
left = l;
right = r;
}
public void setData(E d)
{
data = d;
}
public E getData()
{
return data;
}
public Node<E> getRight()
{
return right;
}
public void setRight(Node<E> nd)
{
right = nd;
}
public Node<E> getLeft()
{
return left;
}
public void setLeft(Node<E> nd)
{
left = nd;
}
public Node<E> getParent()
{
return parent;
}
public void setParent(Node<E> nd)
{
parent = nd;
}
}
Im trying to follow what you said, this is my test class
public class BSTTest
{
public void testInsert()
{
int height;
BST myTree = new BST();
myTree.insert(1);
}
}
but when i compile i get the error of unexpected type, it says if found an int but requires a reference on the line of BST myTree = new BST(); what does that mean?
Yes, make a class called BSTTest and create methods to test each of the public methods in BST.
If you use JUnit, you can use annotations and a standard naming convention
public class BSTTest {
#Test
public void testInsert() {
BST<String> bst = new BST<String>();
String s = "hello";
bst.insert(s);
AssertTrue("I should get back what I put in!", bst.find(s));
}
#Test
public void testDelete() {
// etc...
}
}
Then, you can run this 'Unit Test' in your java IDE (such as IntelliJ IDEA) or, if you have it set up, via maven: mvn test.
Also, I think your find() method could return boolean?
good luck!
Related
An abstract binary tree is to be created using a generic class. Each node has a string value as well as an initialCalculatedValue value. No changes should be made to the main class and a static inner class is to be included in the generic class. I'd like some advice on my code, as the main class is giving me error on accessing 'timesVisited' and 'values'. My code can't seem to access those variables.
Main class code:
public class Main{
public static void main(String[] args) {
WalkableTree<String, Integer> ast = new WalkableTree<>(0);
WalkableTree.Node<String, Integer> plus = ast.setRoot("+");
plus.setRightChild("20");
WalkableTree.Node<String, Integer> multiply = plus.setLeftChild("*");
multiply.setLeftChild("10");
WalkableTree.Node<String, Integer> bracketedPlus = multiply.setRightChild("+");
bracketedPlus.setLeftChild("3");
bracketedPlus.setRightChild("4");
// write visitor to display pre-order
System.out.println("Pre-order traversal:");
ast.walk(current -> {
if(current.timesVisited == 2)
System.out.print(current.value + " ");
});
System.out.println();
// write visitor to display in-order
System.out.println("In-order traversal:");
ast.walk(current -> {
if(current.timesVisited == 3)
System.out.print(current.value + " ");
});
System.out.println();
// write visitor to display post-order
System.out.println("Post-order traversal:");
ast.walk(current -> {
if(current.timesVisited == 4)
System.out.print(current.value + " ");
});
System.out.println();
}
}
Functional interface:
#FunctionalInterface
public interface Visitor<N> {
public void visit(N node);
}
Generic class:
public class WalkableTree <T, R> {
private T root = null;
private R initialCalculatedValue;
public static Node current;
public WalkableTree(R initialCalculatedValue) {
this.initialCalculatedValue = initialCalculatedValue;
}
public Node getRoot() {
return (Node) root;
}
public Node setRoot(T value) {
current = new Node(null,null,null,value,null,0);
return current;
}
public R getInitialCalculatedValue() {
return initialCalculatedValue;
}
public void setInitialCalculatedValue(R initialCalculatedValue) {
this.initialCalculatedValue = initialCalculatedValue;
}
protected void reset(Node node) {
node.timesVisited = 0;
node.calculatedValue = initialCalculatedValue;
reset((Node) node.leftChild);
reset((Node) node.rightChild);
}
public Node nextNode(Node node) {
node.timesVisited++;
if(node.timesVisited == 1)
return node;
if(node.timesVisited == 2)
return (Node) node.leftChild;
if(node.timesVisited == 3)
return (Node) node.rightChild;
if(node.timesVisited == 4)
return (Node) node.getParent();
return node;
}
public void walk(Visitor visitor) {
//Reset all the nodes in the tree
reset((Node) root);
//Set the current node to visit at the root of the tree
visitor.visit(root);
//Walking through the tree as long as the current node still exists
//If current node exists, let the visitor object visit the current node
//Current node is set to the next node using nextNode() method
while (this.current == current)
{
nextNode(current);
}
}
public static class Node<T, R> {
//Variables
Object leftChild;
Object rightChild;
Object parent;
T value;
R calculatedValue;
int timesVisited = 0;
public Node(Object leftChild, Object rightChild, Object parent, T value, R calculatedValue, int timesVisited) {
this.leftChild = leftChild;
this.rightChild = rightChild;
this.parent = parent;
this.value = value;
this.calculatedValue = calculatedValue;
this.timesVisited = timesVisited;
}
public Object getLeftChild() {
return leftChild;
}
public Node setLeftChild(T value) {
Node newLeft = new Node(null,null, current,value,0,0);
current = newLeft;
return current;
}
public Object getRightChild() {
return rightChild;
}
public Node setRightChild(T value) {
Node newRight = new Node(null,null, current,value,0,0);
current = newRight;
return current;
}
public Object getParent() {
return parent;
}
public void setParent(Node parent) {
this.parent = parent;
}
public T getValue() {
return value;
}
public void setValue(T value) {
this.value = value;
}
public R getCalculatedValue() {
return calculatedValue;
}
public void setCalculatedValue(R calculatedValue) {
this.calculatedValue = calculatedValue;
}
public int getTimesVisited() {
return timesVisited;
}
public void setTimesVisited(int timesVisited) {
this.timesVisited = timesVisited;
}
}
}
Update the method in WalkableTree as below:
public void walk(Visitor<Node> visitor) {
//Reset all the nodes in the tree
reset((Node) root);
//Set the current node to visit at the root of the tree
visitor.visit((Node) root);
//Walking through the tree as long as the current node still exists
//If current node exists, let the visitor object visit the current node
//Current node is set to the next node using nextNode() method
while (this.current == current)
{
nextNode(current);
}
}
Implementing LinkedList in a recursive approach was a bit challenging to me, which I get stuck in implementing of its remove method and wonder how to keep reference to previous item in recursive?
MyLinkedList class
package linkedlist;
public class MyLinkedList {
private Integer value;
private MyLinkedList next;
public MyLinkedList() {
}
public MyLinkedList(Integer value) {
this.value = value;
}
public void add(Integer value) {
if (this.value == null) {
this.value = value;
} else if (this.next == null) {
this.next = new MyLinkedList(value);
} else {
this.next.add(value);
}
}
public MyLinkedList remove(Integer index) {
//
// if (index < 0) {
// return this;
// }
// if (index == 0) {
// return this.next;
// }
// this.next = remove(index - 1);
return this;
}
public Integer indexOf(Integer value) {
if (this.value.equals(value)) {
return 0;
} else if (this.next == null) {
return null;
} else {
return 1 + this.next.indexOf(value);
}
}
}
MyLinkedListTester class
package linkedlist;
public class MyLinkedListTester {
public static void main(String[] args) {
MyLinkedList myLinkedList = new MyLinkedList();
myLinkedList.add(1);
myLinkedList.add(2);
myLinkedList.add(3);
myLinkedList.add(4);
System.out.println("Index Of Array: " + myLinkedList.indexOf(3));
MyLinkedList linkedList = myLinkedList.remove(3);
}
}
As mentioned in the comments the iterative approach is easier and more efficient most of the time. Anyway I think you do this as an exercise because in Java you already have a LinkedList.
So first you have a kind of error in your thinking (as far as I'm aware of it). It's also a kind of bad design choice. You create your MyLinkedList and save the data right into it and the next is also of the class MyLinkedList but it's not a list, it's a Node. There should only be one List, and 0 - many nodes.
For example I can't figure out how to do a remove function that will return the removed Node (in your case MyLinkedList) and as well let you keep the list in case you remove the first element in your list.
If you are looking in the implementation that's why they use Nodes and it's also more logical (a list doesn't contain "List elements") and so on...
Some other remark: your indexOf funtion will return an error if you try to get a element that does not exist (1 + null => error).
So anyway. What you have to do is to create a Node. (btw if you really want a real LinkedList you can use generic instead of int/Integer).
Below I post my solution how to do it (may be better out there but that is how I would do it). I also wrote a toString method to see how the List looks like (and it works as far as I can say). In case you want to still use your code without the Node it should give you an idea how to solve your problem with remove. You can also put some of the logic into the Node class but for me Node is only a container and doesn't really contain any logic.
public class MyLinkedList {
private Node head;
public MyLinkedList() {
}
public class Node{
private int value;
private Node next = null;
public Node(int value){
this.value = value;
}
public int getValue(){
return value;
}
public Node getNext(){
return next;
}
public void setNext(Node next){
this.next = next;
}
}
public void add(int value) {
Node next = new Node(value);
if(head == null){
head = next;
} else {
addRecursive(head,next);
}
}
private void addRecursive(Node node, Node next) {
if(node.next == null){
node.setNext(next);
} else {
addRecursive(node.getNext(),next);
}
}
public Node remove(int index){
Node removeNode = head;
if(index == 0){
head = head.getNext();
} else {
removeNode = removeRecursive(head,index-1);
}
return removeNode;
}
private Node removeRecursive(Node node, int index){
Node removeNode = node.getNext();
if(index == 0){
node.setNext(removeNode.getNext());
} else {
removeNode = removeRecursive(node.getNext(),index-1);
}
return removeNode;
}
public int indexOf(int value) {
if (head == null){
return -1;
} else if (head.getValue() == value){
return 0;
} else {
return indexOfRecursive(head,value,0);
}
}
private int indexOfRecursive(Node node, int value, int index) {
if(node.getNext() == null){
return -1;
} else if(node.getNext().getValue() == value){
return index + 1;
} else {
return indexOfRecursive(node.getNext(),value,index+1);
}
}
#Override
public String toString(){
if(head == null){
return "";
} else {
return toStringRecursive(head,"["+head.getValue());
}
}
private String toStringRecursive(Node node, String output){
if(node.getNext() == null){
return output + "]";
} else {
return toStringRecursive(node.getNext(),output + ", " + node.getNext().getValue());
}
}
}
This is my implementation of BST in Java.
public class BST {
Node root;
public BST(){
root = null;
}
// public BST(int item){
// root = new Node(item);
// }
private class Node{
int data;
Node left;
Node right;
public Node(int data){
this.data = data;
this.left = null;
this.right = null;
}
}
public void add(int item){
add(item, root);
}
private Node add(int item, Node p ){
if(p == null){
p = new Node(item);
}
else if(item < p.data) p.left = add(item, p.left);
else if(item > p.data) p.right = add(item, p.right);
return p;
}
public void inorder(){
inorder(root);
}
private void inorder(Node p){
if(p == null) return;
inorder(p.left);
System.out.print(p.data + " ");
inorder(p.right);
}
}
This is the calling code.
public class Main {
public static void main(String[] args) {
// write your code here
//BST bst = new BST(13);
BST bst = new BST();
bst.add(12);
bst.add(7);
bst.add(3);
bst.add(2);
bst.add(19);
bst.add(4);
bst.add(17);
bst.add(11);
bst.inorder();
}
}
The issue here is when I use the BST parameterized constructor, everything works as expected. But if I dont and use the default constructor, the root continues to remain null and nothing gets added. Can't seem to understand why this is happening. The debugger gives a null pointer exception inside the add helper call. But the way my add is defined if a null root is the caller, then there should be no exceptions at all. My question is why is the BST with default constructor not working?
Correct add method like this:
public void add(int item)
{
root = add(item, root);
}
instead of this:
public void add(int item)
{
add(item, root);
}
In this method private Node add(int item, Node p ) you are returning p but then public void add(int item) doesn't store it. So basically whatever object you are returning, doesn't have a reference.
Change:
public void add(int item){
add(item, root);
}
to:
public void add(int item){
if (root == null)
root = add(item, root);
else
add(item, root);
}
So the idea is to make a Double Ended Priority Queue so far I have got a tree like structure using 2 Linked Lists, I have and interface I have to stick with with no alterations to it. The problem I have got is I have to make 2 methods called getMost and getLeast which gets the most or least node and then makes that node null. But these 2 methods are proving quite difficult to make. How would you go about doing it?
I have tried using recursion but this is proving difficult as I have to select the tree by going tree.root but passing in tree.root into a recursive method always starts it from tree.root
Also I have tried what i have written in inspectLeast() and inspectMost() but Java passes by value not by reference. Any tips?
P.S Not allowed to use anything from java collections or java util.
public class PAS43DPQ implements DPQ
{
//this is the tree
TreeNode tree = new TreeNode();
//this is for the size of the array
int size = 0;
#Override
public Comparable inspectLeast() {
return tree.inspectLeast(tree.root);
}
#Override
public Comparable inspectMost() {
return tree.inspectMost(tree.root);
}
#Override
public void add(Comparable c)
{
tree.add(c);
size++;
}
#Override
public Comparable getLeast() {
if (tree.root != null){
}
return getLeast();
}
#Override
public Comparable getMost(){
Comparable most = getMost();
return most;
}
#Override
public boolean isEmpty() {
return (size > 0)?true:false;
}
#Override
public int size() {
return this.size;
}
class TreeNode{
private Comparable value;
private TreeNode left, right, root;
//constructors
public TreeNode() {}
public TreeNode(TreeNode t) {
this.value = t.value;
this.left = t.left;
this.right = t.right;
this.root = t.root;
}
public TreeNode(Comparable c) {
this.value = (int) c;
}
public void add(Comparable input){
if(root == null){
root = new TreeNode(input);
return;
} else {
insert(root, input);
}
}
public Comparable inspectLeast(TreeNode n){
if (n == null)
return null;
if (n.left == null){
TreeNode least = n;
return least.value;
}
return inspectLeast(n.left);
}
public Comparable inspectMost(TreeNode n){
if (n == null)
return null;
if (n.right == null){
TreeNode most = n;
return most.value;
}
return inspectMost(n.right);
}
public Comparable getMost(TreeNode n){
if(n.right == null)
return n.value;
return tree.getMost(right);
}
public void insert(TreeNode n, Comparable input){
if(input.compareTo(n.value) >= 0){
if (n.right == null) {
n.right = new TreeNode(input);
return;
}
else
insert(n.right, input);
}
if(input.compareTo(n.value) < 0){
if(n.left == null) {
n.left = new TreeNode(input);
return;
}
else
insert(n.left, input);
}
}
}
}
You should be able to modify your TreeNode.getMost(TreeNode n) and TreeNode.getLeast(TreeNode n) similar to the following:
public class TreeNode{
// Also, your parameter here seems to be superfluous.
public TreeNode getMost(TreeNode n) {
if (n.right == null) {
n.root.right = null;
return n;
}
return n.getMost(n);
}
}
Get least should be able to be modified in a similar fashion, but using left rather than right obviously.
Im trying to test a java generic class that i wrote, this is my test
public class BSTTest
{
public void testInsert()
{
int height;
BST<int> myTree = new BST<int>();
myTree.insert(1);
}
}
but when i compile i get the error of unexpected type, it says if found an int but requires a reference on the line of BST myTree = new BST(); what does that mean?
below are my Binary search tree and node class for reference
public class BST<E extends Comparable<E>>
{
public Node<E> root;
public BST()
{
root = null;
}
//insert delete find height
public void find(E s, Node<E> n)
{
//empty tree, root is null
if(n == null)
{
System.out.println("Item not present.");
}
//n is the node where s is, return n
else if(n.getData().equals(s))
{
System.out.println("Item present");
}
//s is greater than n, look for s on the right subtree
else if(s.compareTo(n.getData()) > 0)
{
find(s, n.getRight());
}
//s is less than n, look for s on the left subtree
else
{
find(s, n.getLeft());
}
}
public int height()
{
int count;
return count = height(root);
}
private int height(Node<E> n)
{
int ct = 0;
if(n == null)
{
}
else
{
int left = height(n.getLeft());
int right = height(n.getRight());
ct = Math.max(left, right) + 1;
}
return ct;
}
public void insert(E s)
{
root = insert(s, root);
}
private Node<E> insert(E s, Node<E> T)
{
//easiest case, empty tree, create new tree
if(T == null)
{
T = new Node<E>(s,null,null);
}
//easiest case, found s
else if(s.compareTo(T.getData()) == 0)
{
System.out.println("Item already present.");
}
//s is greater than T, insert on right subtree
else if(s.compareTo(T.getData()) > 0)
{
T.setRight(insert(s, T.getRight()));
}
//s is less than T, insert on left subtree
else
{
T.setLeft(insert(s,T.getLeft()));
}
return T;
}
public void delete(E d)
{
}
}
and my node class
public class Node<E>
{
private E data;
private Node<E> left;
private Node<E> right;
private Node<E> parent;
public Node(E d, Node<E> r, Node<E> l)
{
data = d;
left = l;
right = r;
}
public void setData(E d)
{
data = d;
}
public E getData()
{
return data;
}
public Node<E> getRight()
{
return right;
}
public void setRight(Node<E> nd)
{
right = nd;
}
public Node<E> getLeft()
{
return left;
}
public void setLeft(Node<E> nd)
{
left = nd;
}
public Node<E> getParent()
{
return parent;
}
public void setParent(Node<E> nd)
{
parent = nd;
}
}
Can you try Integer instead of int?
Generic type takes only Classes (Object types) and not the primite data type
It should be
BST<Integer> myTree = new BST<Integer>();
Java generics are only for Object types. Since, int is a primitive type you cannot use it. Instead use BST<Integer>
You can't use a primitive type like int as a parameter to a generic class in Java. It has to be a class type, such as Integer.