CODEWITHSUNDEEP
java
the_prole
the_prole

Reputation: 8985

Type incompatibility error using generics

I have this linked list class implementation LinkedList which contains a method getMode

public class LinkedList<AnyType extends Comparable<? super AnyType>>
{

    //Some code...

    public AnyType mode(){

        //Some code...

            ListNode node;
            AnyType mode;

            mode = node.element;
            return mode;
    }
}

The generic variable AnyType is type bound in this linked list class. The same variable is bound in another class ListNode. ListNode is not declared in LinkedList. It is an independent class.

class ListNode<AnyType extends Comparable<? super AnyType>>
{

    //Some code...

    public AnyType   element;
}

I'm wondering why the line in the linked list class 

mode = node.element;

Is giving me a type incompatability error

>Required AnyType
Found java.lang.Comparable < >

The type bounds for the generic AnyType variable is the same in both the node class and the linked list class, so I dont' see why there should be type incompatability here.

The type bound is always 

 <AnyType extends Comparable<? super AnyType>>

edit

Someone has mentioned a solution which appears to work. I had to specify AnyType as a bound for the node node variable in the getMode method, otherwise the raw type was used or something like that

public class LinkedList<AnyType extends Comparable<? super AnyType>>
    {

        //Some code...

        public AnyType mode(){

            //Some code...

                ListNode<AnyType> node; // <--- here
                AnyType mode;

                mode = node.element;
                return mode;
        }
    }

Upvotes: 0

Views: 60

Answers (1)

Darth Android
Darth Android

Reputation: 3502

Because the compiler doesn't know that AnyType from your LinkedList is the same as the AnyType in your ListNode

For example, LinkedList<String> and ListNode<Integer> are both valid (satisfy the bounds upon AnyType), but you would probably run into a bunch of issues if a LinkedList<String> was handling ListNode<Integer>s.

You need to make sure that any ListNodes inside of your LinkedList class are all declared as ListNode<AnyType>.

Side note, the common Java convention would be to use E instead of AnyType as the name of the generic element type in a collection.

Upvotes: 2

Related Questions