Re: generics and arrays and multi-class collections

On Sep 29, 5:38 pm, xen <x...@xxxxxxxxxx> wrote:
Yo peoples of the earth,

What is the proper use of generics when you want to use arrays as
well?
Is there anybody out there that writes code that does NOT generate
unchecked warnings?

For example, java.util.ArrayList uses an array of Object to store its
elements, and uses a cast (E)elements[i] to retrieve them, which
generates an unchecked warning. I myself have wanted to use an array
of generified sets, so I just create a Set[] and assign it to a
Set<E>[], which generates a warning. I can trim down on the warnings
so that I only get "unchecked conversion" and "unchecked cast"
warnings, but it seems I'll have to live with those.

My last addition was a Map that can store Lists that store different
classes that are all decendants of a superclass:

Map<Class<? extends Feature>, List<? extends Feature>> stores;
stores = new HashMap<Class<? extends Feature>, List<? extends
Feature>>();

I want a method that retrieves each store, and creates one if not
present.

public <F extends Feature> List<F> getStore(Class<F> c) {
List<F> L = (List<F>)stores.get(c); // unchecked cast
if (L == null) {
L = new ArrayList<F>();
stores.put(c, L);
}
return L;
}

The cast generates an unchecked warning.

Now given
class Block extends Feature {}
I can do
List<Block> = getStore(Block.class);
which is what I wanted.

What are your experiences, any advice?

greetings, xen.

In my opinion, using Arrays is akin to the "primative obsession" anti-
pattern. You'd probably be better off using a List<Set<T>> or simply
List<T>, depending on your needs.

The little bit of overhead you incur is *far* outweighed by the
functionality gained.


.

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