Java : How do I implement a generic Binary Search Tree?

Question

Until now, I have been writing a Node class as

class Node {
        private  value;
        private Node left;
        private Node right;

        public int getValue() {
            return value;
        }

        public void setValue(int value) {
            this.value = value;
        }

        public Node getLeft() {
            return left;
        }

        public void setLeft(Node left) {
            this.left = left;
        }

        public Node getRight() {
            return right;
        }

        public void setRight(Node right) {
            this.right = right;
        }
    } 

and Binary Search Tree as

public class BinarySearchTree {
    private Node root;

    public BinarySearchTree(int value) {
        root = new Node(value);
    }

    public void insert(int value) {
      Node node = new Node(value);
        // insert logic goes here to search and insert
    }
}

Now I would like to support BinarySearchTree to have insert node of any type like strings, people

How can I make it generic to hold any type?

Answer 1

Just make each of the Node and BinarySearchTree classes generic:

class Node<T extends Comparable<T>> {
    private T value;
    private Node<T> left;
    private Node<T> right;

    public Node(T value) {
        this.value = value;
    }

    public T getValue() {
        return value;
    }

    public void setValue(T value) {
        this.value = value;
    }

    public Node<T> getLeft() {
        return left;
    }

    public void setLeft(Node<T> left) {
        this.left = left;
    }

    public Node<T> getRight() {
        return right;
    }

    public void setRight(Node<T> right) {
        this.right = right;
    }
} 

and:

class BinarySearchTree<T extends Comparable<T>> {
    private Node<T> root;

    public BinarySearchTree(T value) {
        root = new Node<T>(value);
    }

    public void insert(T value) {
      Node<T> node = new Node<T>(value);
        // insert logic goes here to search and insert
    }
}

Note the Comparable extension constraint that you will need later to enforce node ordering in the tree. Thanks to zaske for the suggestion.

Answer 2

Please find the BST using Generics, U can find more information on below link 

https://www.cs.cmu.edu/~adamchik/15-121/lectures/Trees/code/BST.java

public class BinarySearchTree< T extends Comparable<T>> {
    Node root;
    class Node {
        T data;
        Node left;
        Node right;

        public Node(T data) {
            this.data = data;
        }
    }

    public boolean isEmpty() {
        return root == null;
    }

    public void insert(T value) {
        if(isEmpty())
            root = new Node(value);
        else
            insert(root, value);
    }

    private void insert(Node node, T value) {

        if(value.compareTo(node.data) < 0) {
            if(node.left == null)
                node.left = new Node(value);
            else
                insert(node.left, value);
        }
        else {
            if(node.right == null)
                node.right = new Node(value);
            else
                insert(node.right, value);
        }
    }

}