How to fix 'Bound mismatch' in Java

Question

I try to extend the AbstractTreap class in my Treap class with the generics.

I downloaded the TreapNode and AbtractTreap file and try to implement the Treap class as some exercise.

The result should be a Treap like here: https://www.geeksforgeeks.org/treap-a-randomized-binary-search-tree/

public class Treap<E> extends AbstractTreap<E>

public final class TreapNode<E extends Comparable<? super E>> 
       implements Comparable<TreapNode<E>>, java.util.Comparator<TreapNode<E>>

public abstract class AbstractTreap<E extends Comparable<? super E>>

Error:

Bound mismatch: The type E is not a valid substitute for the bounded parameter > of the type AbstractTreap

Answer 1

AbstractTreap has a generic parameter that is a Comaparable . If you extend it and pass that parameter, you must make sure it stands for at least the same bounds (if not more restrictive). Eg:

public class Treap<E extends Comparable<? super E>> extends AbstractTreap<E>