CODEWITHSUNDEEP
javagenericslinked-liststack
user3371034
user3371034

Reputation: 21

Bound Mismatch Linked List Java

I am working on an assignment to make a stack in java using Linked Lists, but there is an error I am getting, which prevents me from doing anything. here is first of all the Node class 

public class SortedLinkedSetNode<T extends Comparable<T>>{
    protected T value;
    protected  SortedLinkedSetNode<T> next;
    // other methods
}

now here is the Stack class , of which I will only give the Push method because an error occurs there.

 public class StackList<E> implements Stack<E> {
     protected SortedLinkedSetNode upperMost;
     public void push( E element) {
        SortedLinkedSetNode <E> newNode = new SortedLinkedSetNode (element);
        newNode.next = upperMost;
        upperMost = newNode;    
    }
}

the problem is that when i try to make the newNode inside Push i get this message : 

Bound mismatch: The type E is not a valid substitute for the bounded parameter <T extends Comparable<T>> of the type  SortedLinkedSetNode<T>

I tried modifying the stack class so that it is 

public class StackList<E extends Comparable<E>> implements Stack<E> {

but i am NOT allowed to modify it (thats just the assignment specification). I also tried using T not using anything and all sorts of combinations but there is always an error. I think that it all comes from this (which is given)

public class SortedLinkedSetNode<T extends Comparable<T>>{

but am not sure, and also not sure what to do if it really is from here
Can someone help me out with what exactly this is , and how i could solve it. If i can't make a new node in the stack class how can i even begin doing Push Pop etc.. ? Thank you

Upvotes: 0

Views: 469

Answers (2)

rgettman
rgettman

Reputation: 178263

You have made your SortedLinkedSetNode class generic, with an upper bound on T. However, when you attempt to use the class with E in StackList, you didn't declare E with the same upper bound, resulting in a bound mismatch. Try adding the upper bound to E on StackList:

public class StackList<E extends Comparable<E>> implements Stack<E> {

Also, the SortedLinkedSetNode class is generic, but you are inconsistently applying a generic type parameter to your code that uses the class.

When declaring the variable upperMost, use <E>:

protected SortedLinkedSetNode<E> upperMost;

Additionally, add <E> to when you create a new SortedLinkedSetNode (could be the diamond "operator" <> if you're using Java 1.7+).

SortedLinkedSetNode<E> newNode = new SortedLinkedSetNode<E> (element);

Upvotes: 1

m0skit0
m0skit0

Reputation: 25873

"The type E is not a valid substitute for the bounded parameter > of the type SortedLinkedSetNode" means that E is more generic than T extends Comparable<T>. You're declaring that your generic type T must extend Comparable<T>, while <E> doesn't have such limitation, and as such, E is invalid for your SortedLinkedSetNode<T extends Comparable<T>>.

If you can't modify the Stack class, then you have no choice than to change your class to

public class SortedLinkedSetNode<T>

Also you need to use <E> in your object instantiation

new SortedLinkedSetNode<E>(element);

Upvotes: 0

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