为什么我的二进制搜索树不会显示超过3个节点？

Question

My Binary Search Tree cant seem to manage more then 3 nodes or be able to display them. I needed to add them iterably and display them using a stack in the assignment but am having trouble displaying the BST if it has more then 3 elements.

public boolean add(E b) {

    //if tree is empty
    if (root == null) {
        root = new Node();
        root.setValue(b);
        count++;
        return true;
    } //if val is already in tree
    else if (b.compareTo(root.getValue()) == 0) {
        return false;
        //if left or right spot is free
    } else {
        while (root != null) {
            compareResult = root.value.compareTo(b);
            spot = root;
            if (compareResult < 0) {
                if (root.left != null) {
                    spot = spot.left;
                    count++;
                    return true;
                } else {
                    Node n = new Node<>();
                    n.setValue(b);
                    spot.left = n;
                    count++;
                    return true;
                }
            } else if (compareResult > 0) {
                if (root.right != null) {
                    spot = spot.right;
                    count++;
                    return true;
                } else {
                    Node n = new Node<>();
                    n.setValue(b);
                    spot.right = n;
                    count++;
                    return true;

                }
            } else {
                return false;
            }
        }
    }
    return false;

}

public void display() {
    //needs to use an iterator
    if (root == null) {
        System.out.println("Error");
    } else {
        Node CurrentNode;
        CurrentNode = root;
        while (!stack.isEmpty() || CurrentNode != null) {
            if (CurrentNode != null) {
                stack.push(CurrentNode);
                CurrentNode = CurrentNode.right;


            }
            else {
                Node m= stack.pop();
                System.out.println(m.value);
                CurrentNode = m.left;
            }

        }
    }
}

public int size() {
    return count;
}

@Override
public int compareTo(E t) {
    return ordering.compare(root,t);
}

@Override
public int compare(E t, E t1) {
    return t.compareTo(t1);
}

The Node class looks like this

public class Node<E extends Comparable> {

E value;
Node<E> left;
Node<E> right;

//constructor
public Node() {
    value = null;
    left = null;
    right = null;


}

public void setValue(E t) {
    value = t;
}

public void setLeft(Node<E> t) {
    left = t;

}

public void setRight(Node<E> t) {
    right = t;
}

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

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

public E getValue() {
    return value;
}

Answer 1

I can see a couple of changes that you need to make.

After the } else { line in your add method, you should swap the next three lines around, to have

  spot = root;
  while (spot != null) {
        compareResult = spot.value.compareTo(b);

because spot is going to track its way down the tree while you iterate the loop. But because you're currently using root instead of spot , you're always comparing values with the root node, instead of lower down nodes.

Also, remove count++; and return true; from after spot = spot.left; and spot = spot.right; , because in these cases, you haven't actually added anything to the tree, so you need to continue on through the loop.