CODEWITHSUNDEEP
javabinary-search-tree
Sphyxx
Sphyxx

Reputation: 15

Binary Search Tree having issues with recognising when making root node

Trying to make a root in this BST as such:

if (currentNode == null) {
            currentNode = new BinaryNode(newInt);
            System.out.println(currentNode);
            System.out.println(newInt);
            //System.out.println(newInt.getValue());
            System.out.println("Node Null, made root");
         }else{

The println is there for debugging. However I'm having issues as this is the output:

BinaryNode@7004ba66
4
Node Null, made root
BinaryNode@4669b7fe
6
Node Null, made root
BinaryNode@46aea8cf
1
Node Null, made root
BinaryNode@74ccd249
3
Node Null, made root
BinaryNode@3301f287
2
Node Null, made root
BinaryNode@44d9973a
8
Node Null, made root
BinaryNode@29578426
7  
Node Null, made root
BinaryNode@30a4effe
5
Node Null, made root
BinaryNode@1c8825a5
9
Node Null, made root

Which makes me think it isn't recognising (currentNode == null) like it should. Any ideas why?

full pastebin: here

Any help greatly appreciated :)

Upvotes: 0

Views: 102

Answers (2)

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726489

The problem is that when you assign currentNode, root does not get assigned.

Java passes variables by value, meaning that a copy of the value or a reference gets passed into your method. In this case, currentNode, a formal parameter of your insertNode method, is passed a copy of the root field returned by the getRoot method.

To fix this, you should split the insertNode method in two:

public void insert(int newInt);

and

private BinaryNode insert(int newInt, BinaryNode node);

The public method should be used without getRoot parameter (the users of your class inserting in the tree should never need to pass the root, otherwise they would be able to break your tree by passing a node in the middle with numbers that should go in a different branch).

The private method should return the old or the new node. You should be using it like this:

public void insert(int newInt) {
    root = insert(newInt, root);
}

The method itself should return new node if node passed in is null. When node is not null, the method should return the node passed in.

As far as the outputList problem goes, you should use StringBuffer instead of String to construct the output. Unlike String which is immutable, StringBuilder is mutable. It lets you change the string inside it (use append instead of +=).

Upvotes: 2

Vincent van der Weele
Vincent van der Weele

Reputation: 13177

You are not assigning to the root of your tree. Change it to:

if (root== null) {
        root= new BinaryNode(newInt);

Upvotes: 1

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