CODEWITHSUNDEEP
java
user3256369
user3256369

Reputation: 137

compareTo is asking me to cast, and I do not know why

Can someone explain why I am getting this error: The method compareTo(AVLNode) is undefined for the type AVLNode

Here is a shortened version of my Tree class:

public  class AVLTree< E extends Comparable<E> >
{
    private AVLNode<E> root ;

    public AVLTree()  
    {
        this.root = null;
    }

    public void insert ( AVLNode<E>  item ) 
    {  
        if( item.getLeft().compareTo(item.getItem() ) < 0) //ERROR IS HERE
        {
        }
    }  

}

Below is my a short version of my Node class

class AVLNode <E extends Comparable<E> >   
{   
private AVLNode<E>  item;
private AVLNode<E>  left;   

public AVLNode ( AVLNode<E> item) 
{  
    this.item = item;
    this.left = null;
}  

public AVLNode( AVLNode<E> item, AVLNode<E> lft ) 
{
    this.item = item;
    this.left = lft;
}

public AVLNode<E> getItem()
{
    return this.item;
}
public AVLNode<E> getLeft()
{
    return this.left;
}

}

Upvotes: 1

Views: 153

Answers (4)

ifloop
ifloop

Reputation: 8386

Your AVLNode class should obviously look like this:

public class AVLNode<E extends Comparable<E>> {
    private E item;

    //...

    public int compareTo(final E obj) {
        return this.item.compareTo(obj);
    }

Difference:

  • item should be of type E not AVLNode<E> because you want to store an E and not a AVLNode.

To state, that your AVLNodes are comparable, they could implement Comparable<T> themself by just delegating to E#compareTo() method:

public class AVLNode<E extends Comparable<E>> implements Comparable<AVLNode<E>> {
    private E item;

    //...

    @Override
    public int compareTo(final AVLNode<E> other) {
        return this.item.compareTo(other.item);
    }
}

Upvotes: 1

posdef
posdef

Reputation: 6532

That's because AVLNode doesn't have a method called compareTo() if you implement one then the issue should be solved.

You should also decide whether your want to compare E vs E or AVLNode vs AVLNode

Upvotes: 0

khelwood
khelwood

Reputation: 59104

getLeft() returns an AVLNode. You try and call getLeft().compareTo(...). This requires that AVLNode provides a matching method.

From this:

class AVLNode <E extends Comparable<E> >   
{   
    private AVLNode<E>  item;
    ...

It looks like your nodes can only hold other nodes. Presumably your items should actually be of the comparable type E. Then you can retrieve the item and call compareTo() on that.

Upvotes: 0

Ashley Frieze
Ashley Frieze

Reputation: 5443

Your Comparable base class assumes you're comparing to Es when you want to compare to AVLNode<E>s

So change it to inherit Comparable<AVLNode<E>> and see what happens.

Upvotes: 3

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