Why do I get incompatible types when I am giving ? extends in both class and return

Question

In one of my classes I have...

public Class<? extends Map<K, V>> getObjectType() {
    return (Class<? extends Map<K, V>>) Map.class;
}

What is wrong with this code

I keep getting

error: incompatible types: Class <Map> cannot be converted to Class<extends Map<K,V>>
    return (Class<? extends Map<K, V>>) Map.class;

Can someone point me in the right direction

[This](http://stackoverflow.com/questions/4343202/difference-between-super-t-and-extends-t-in-java) should answer your question — Robin Topper, Apr 28 '17 at 15:46
What should `Class extends Map>` represent in the first place? There is no class `Map` only `Map` due to type erasure. — Thomas, Apr 28 '17 at 16:11

score 0 · Answer 1 · answered Apr 28 '17 at 17:49

K and V aren't actual types and would be erased by type erasure anyway. Just use Map. And there is no need to cast. You only cast to a more specific type and Map.class is an instance of Class<? extends Map>.

public Class<? extends Map> getObjectType() {
    return Map.class;
}

other examples using compatible types:

public Class<? extends Map> getObject1Type() {
    return HashMap.class;
}

public Class<? extends Map> getObject2Type() {
    return LinkedHashMap.class;
}

Why do I get incompatible types when I am giving ? extends in both class and return

1 Answers1