Creating a Generic Binary Search Tree in Java

Question

I'm trying to create this Tree in Java but am stuck and can't figure out how to continue. Here is the code I have so far:

public class BTNode<E>
{
private E data;
private BTNode<E> left;
private BTNode<E> right;

public BTNode(E newData, BTNode<E> newLeft, BTNode<E> newRight)
{
    setData(newData);
    setLeft(newLeft);
    setRight(newRight);
}

public E getData()
{
    return data;
}

public BTNode<E> getLeft()
{
    return left;
}

public BTNode<E> getRight()
{
    return right;
}

public void inorderPrint()
{
    if(left != null)
        left.inorderPrint();

    System.out.println(data);

    if(right != null)
        right.inorderPrint();
}

public void setData(E newData)
{
    data = newData;
}

public void setLeft(BTNode<E> newLeft)
{
    left = newLeft;
}

public void setRight(BTNode<E> newRight)
{
    right = newRight;
}

}

public class Tree<E extends Comparable<E>>
{
private BTNode<E> root;
private int manyNodes;

public Tree()
{

}

public void add(E element)
{
    BTNode<E> newLeft = null;
    BTNode<E> newRight = null;

    if(root == null)
        root = new BTNode<E>(element, newLeft, newRight);

    else
    {
        BTNode<E> cursor = new BTNode<E>(element, newLeft, newRight);
        cursor = root;
        boolean done = false;

        while(done = false)
        {
            if (element.compareTo(cursor.getData()) <= 0)
            {
                if(cursor.getLeft() == null)
                {
                    cursor.setLeft(element); //create a new node from left
                    done = true;
                }

                else
                    cursor = cursor.getLeft();
            }

            else
            {
                if(cursor.getRight() ==null)
                {
                    cursor.setRight(element); //create a new node from right
                    done = true;
                }
                else
                    cursor = cursor.getRight();
            }
        }
    }

}

public int size()
{
    return manyNodes;
}

public BTNode<E> getRoot()
{
    return root;
}

}

The problem is creating the left and right nodes, it's not letting me because the types are different. Also i'm not sure what to put in the Tree constructor.

Sotirios Delimanolis · Accepted Answer · 2013-11-13 03:46:17Z

1

The methods

public void setLeft(BTNode<E> newLeft) {
    left = newLeft;
}
public void setRight(BTNode<E> newRight) {
    right = newRight;
}

are expecting BTNode objects but you are calling them like

cursor.setLeft(element);

where element is of type E and E is, as far as the compiler is concerned, a type that extends Comparable<E>. You have a type mismatch. Wrap your element in a BTNode object and pass that.

answered Nov 13, 2013 at 3:46

Sotirios Delimanolis

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4 Comments

user2985986 Over a year ago

You mean like this: cursor.setLeft((BTNode<E>)element);

Sotirios Delimanolis Over a year ago

@user No, that is called casting. I mean create a new BTNode object and give it the element as its data.

user2985986 Over a year ago

BTNode<E> left = new BTNode<E>(element, null, null); ? I'm still not following. I'm trying to create a new node for the left, not the data. sorry

Sotirios Delimanolis Over a year ago

@user2985986 There are many things wrong with your add method. First, the comparison operator is == not =. Second, you immediately re-assign the cursor variable that previously store the node you want to add.

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