class Fruit {...}
class Apple extends Fruit implements Comparable<Apple> {...}
// apples are only comparable to apples

class Fruit implements Comparable<Fruit> {...}
class Apple extends Fruit {...}
// comparable to any fruit or subclass

//to accommodate the second example:
<T extends Comparable<? super T>> T max(Collection<? extends T> coll)
// the type parameter is read as: my type is a subtype of a Comparable that takes in and return a type that is a supertype to T