It seems you have a class LinkedList declared as
class LinkedList<T extends Comparable<T>> {...}
but you're trying to use it in a class Stack declared as
class Stack<T> {
private LinkedList<T> list;
...
}
The type variable T declared in Stack is completely unrelated to the type variable T in LinkedList. What's more, they are not compatible. LinkedList expects a type that is a sub type of Comparable, but Stack is giving it a type argument that has no bounds. The compiler cannot allow this.
Add appropriate bounds to your Stack class' type parameter
class Stack<T extends Comparable<T>> {
