Generic Lower bounded Method

Question

Let's say I have the following classes Animal, Fish, and CatFish.

CatFish extends Fish and Fish extends Animal.

There is a generic class called MyPets, which has a type parameter (generic) called T, and that will be parameterized with the above classes' objects.

My question is, how do I create a lower bounded method in D that will take any objects that is a PARENT class of the CatFish class.

[This](http://stackoverflow.com/questions/8403489/java-generic-methods-super-cant-be-used) may help. — Boris the Spider, Mar 20 '13 at 23:08
What's `D`? Is it important, or could this method be declared anywhere? — Paul Bellora, Mar 21 '13 at 00:20

score 1 · Accepted Answer · answered Mar 21 '13 at 13:28

You can't.

TL;DR:

Type parameters can have several bounds, like in class Box {...} . But a type parameter can have no lower bound, that is, a construct such as class Box {...} is not permitted. Why not? The answer is: it is pointless because it would not buy you anything, were it allowed.

score 1 · Answer 2 · answered May 16 '17 at 16:37

1

You Can.

Its just the the use of such Lower Bound Generics is debatable and not encouraged. basic use :

public void treatAnimalWhichIsCatFishOrSuperType(Animal<? super CatFish> catFishOrParent){
}

There are other alternatives when you want to return an instance of a generic type from this method, but you can find that in above link.

answered May 16 '17 at 16:37

DevdattaK

198
9

Note that the `? super CatFish` is not precisely a *type parameter* of the method, it's a wildcard for the type parameter of the method's (regular) *parameter*. Lower bounds on type parameters, strictly speaking, aren't allowed, as the other answer states. – Anakhand Mar 30 '20 at 14:06

Generic Lower bounded Method

2 Answers2