Question

My teacher told us that there is a default class in Java for binary tree. I found this BinaryTree class and I tried to declare a BinaryTree object, but it didn’t work.

How can I declare a BinaryTree using this class and which library should I include?

I wrote something like this:

private BinaryTree<Integer> c=new BinaryTree<Integer>();

but it says that BinaryTree cannot be resolved to a type.

Answer 1

Well that class is certainly not the “default java one”. I guess your teacher might be talking about TreeSet which is based on a form of self-balancing binary tree.

I’m not sure how old the class the link you give is but it’s not using generics so it’s probably Java 1.4-. Also, it’s using the default package – which is a bit of a Java no-no, suggesting it might not be production ready. The constructor expects a Comparator which can compare the instances that the tree will store. For example if you want to store Integers in order, you could declare a binary tree as:

BinaryTree bt = new BinaryTree(new Comparator(){
    public int compare(Object a, Object b){
        return ((Integer) a).intValue() - ((Integer) b).intValue();
    }
});

The code above declares an anonymous class which implements the Comparator interface. Alternatively you can use a regular class to do the same thing:

MyIntegerComparator comparator = new MyIntegerComparator();    
BinaryTree bt = new BinaryTree(comparator);

Where you have the code..

class MyIntegerComparator implements Comparator {
    public int compare(Object a, Object b){
        return ((Integer) a).intValue() - ((Integer) b).intValue();
    }
}