BinaryTree implementation

Question

I want to implement a Binary Tree in java and i have a problem with the nodes.The problem is that i can't save the newN in the root node. Everytime i try to insert a new node, the root is null and the pointer doesn't point to the newN address.When i find a node that is null i want to make him point to a newN(a node with info==x and left and right children on null).How can i fix this?

public class Node {
    public int info;
    public Node left;
    public Node right;

    Node(int info) {
        this.info = info;
    }
}



public class BTree {
    public Node root;

    BTree() {
        root = null;
    }

    public void add(int x) {
        insert(root, x);
    }

    public boolean insert(Node r, int x) {
        if (r == null) {
            r = new Node(x);
            return true;
        }
        else{
            if (r.info == x) {
                System.out.println("the value has already been added");
                return false;
        }
            if (r.info < x)
                insert(r.left, x);
            if (r.info > x)
                insert(r.right, x);
        }

        return false;
    }

    public void inOrder() {
        inOrderTraverse(root);
    }

    public void inOrderTraverse(Node r) {
        if (r != null) {
            inOrderTraverse(r.left);
            System.out.print(r.info + " ");
            inOrderTraverse(r.right);
        }

    }

}



    public class Main {
        public static void main(String args[]){
            BTree bt=new BTree();
            bt.add(10);
            bt.add(5);
            bt.add(3);
            bt.add(2);
            bt.inOrder();
        }
    }

PS:I know there are no pointers in Java and all the function calls are made with the address , not the value.Isn't insert(Node r,int x) equivalent with insert(Node &r,int &r) from c++?

score 0 · Accepted Answer · edited May 23 '17 at 11:48

Basically, no insert(Node r, int x) is not equivalent to insert(Node &r, int &x). Java passes arguments by value, not by reference. More to the point here:

public boolean insert(Node r, int x) {
    if (r == null) {
        r = new Node(x);
        return true;
    }
    else{
        if (r.info == x) {
            System.out.println("the value has already been added");
            return false;
    }
        if (r.info < x)
            insert(r.left, x);
        if (r.info > x)
            insert(r.right, x);
    }

    return false;
}

You assume that assigning a value to r (new Node(x)) will assign a value to the location pointed to by r, but this is not how Java understands things. Assigning a value to r will overwrite the value of r, i.e., r now refers to the new Node, but only r as localised to the insert() function. So r no longer has any connection to the original value that was passed in.

You can implement something correctly much more simply:

public void add(int x) {
    if (this.root == null) {
        this.root = new Node(x);
    } else {
        r = this.root;
        if (x > r.info) {
             while (r != null && x > r.info) {
                 r = r.right;
             }

             r.right = new Node(x);
        }
        // similarly for x < root.info, etc.
}

BinaryTree implementation

1 Answers1