CODEWITHSUNDEEP
javagenerics
Othisdede
Othisdede

Reputation: 21

How to fix "method not applicable to arguments" problem in this code that uses generics

I am trying to implement an iterate method to my linked list to make it more readable and more compact since it is used more than once. My problem with the code I assume is not properly understanding Java generics in terms of method declaration. This is the error I'm getting:

Exception in thread "main" java.lang.Error: Unresolved compilation problem: The method iterate(Nodes<T extends Nodes<T>>) in the type LinkedList<T> is not applicable for the arguments (Nodes<T>)

I tried messing around with expected datatypes and arguments but couldn't figure out what is the problem exactly. I checked some other questions but couldn't necessarily find what I asked for or maybe couldn't understand the explanations.

  public class LinkedList<T> extends ListTemplate<T>
     {
       Nodes<T> head;
       Nodes<T> tail;
//declaration of method
       private <T extends Nodes<T>> Nodes<T> iterate(Nodes<T> head)
     {
    Nodes<T>iterate=head;
    while(iterate.getNext()!=null)
     {
        iterate=iterate.getNext();
     }
    return iterate;
     }
//the method call
public void Enqueue(T data)
    {
        Nodes<T>new_node=new Nodes<T>(data);
        //head is set for null when list is empty
        if(head==null)
        {
        //if the list is empty both head and tail will box new_node
        head=new_node;
        tail=new_node;
        }
        //if we insert something to list head wont be null
        else if(head!=null)
        {
        tail=iterate(head);
        tail.setNext(new_node);
        }
}

The code works when I don't try to make a separate method and implement in code. The expected result making this method iterate through the list of nodes I provided and return the last node. I am not sure about my mistake, but probably a declaration is problematic.

Upvotes: 1

Views: 88

Answers (2)

Andy Thomas
Andy Thomas

Reputation: 86411

You're saying that T is both the type of the content of a node, and the type of the returned Nodes object.

   private <T extends Nodes<T>> Nodes<T> iterate(Nodes<T> head)

You could fix by saying this instead:

   private Nodes<T> iterate(Nodes<T> head)

Upvotes: 0

rgettman
rgettman

Reputation: 178263

With this line:

private <T extends Nodes<T>> Nodes<T> iterate(Nodes<T> head)

You're declaring the iterate method to be generic, with its own T type parameter, which is different from the class LinkedList's type parameter T.

Like the Enqueue method (which would normally be spelled in lowercase as enqueue), the iterate method can simply use the class-scoped T defined already. Remove the T declaration on the iterate method:

private Nodes<T> iterate(Nodes<T> head)

Upvotes: 2

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