Binary search tree Tree Implementation, Program terminates in eclipse. simple insert and display operation

Question

This is a class Trees simply to implement the binary search tree, can't understand whats wrong with this.. The class Node is defined separately whose default constructor I have called from here:

public class Trees {

    static Node root = null;

    static void insert(int data, Node r)
    {
        if(r==null)
        {
            r = new Node();
            r.data = data;
            r.left = null;
            r.right=null;
        //  System.out.println(root.data);
        }

        else
        {   
            Node current;
            current = r;

            if(data >=current.data)
                {
                insert(data,current.right);
                }

            else if(data < current.data)
            {
            insert(data,current.left);
            }
        }
    }


    static void display(Node r)
    {

       if(r!=null)
       {

        display(r.left);
        display(r.right);
        System.out.print(r.data +"  ");

       }

    }

    public static void main(String[] args) {

        insert(2, root);
        insert(6, root);
        insert(1, root);
        insert(5, root);

        display(root);

    }

}

What could be wrong with this?

Answer 1

public class Trees {

static Node root = null;

static Node insert(int data, Node r)
{
    if(r==null)
    {
        r = new Node();
        r.data = data;
        r.left = null;
        r.right=null;
        return r;
    //  System.out.println(root.data);
    }

    else
    {   

    Node current=r;
        if(data >=current.data)
            {
          current.right= insert(data,current.right);
            }

        else if(data < current.data)
        {
        current.left=insert(data,current.left);
        }
    }
    return r;

}


static void display(Node r)
{

   if(r!=null)
   {

    display(r.left);
    display(r.right);
    System.out.print(r.data +"  ");

   }

}

public static void main(String[] args) {

    root=insert(2, root);
    root=insert(6, root);
    root=insert(1, root);
    root=insert(5, root);

    display(root);

}

}

class Node
{
     public int data;
     public Node left;
     public Node right;
}

This code is working, If you want to use recursion then you have to assign value of the reference to the reference variable as well. Try this code , this code is working and printing output as well.

          I hope I helped you.

Answer 2

The problem is that in your code root is never assigned to. That is why it works in the code which returns r and assigns to root in the other answer.

static void insert(int data, Node r)
{
    if(r==null)
    {
        r = new Node();
        r.data = data;
        r.left = null;
        r.right=null;
    //  System.out.println(root.data);
    }
    ....
 }

That if block doesn't actually do anything useful. "r" is not passed into the function by reference so the assignment to "r" does not propagate back to the root variable.