如何使用List <? extends Map<String, ?> &gt;

Question

I'm trying to use a constructor of a library i'm using. But i need to pass it this object :

 List<? extends Map<String, ?>>

But i have only an object :

 data = ArrayList<MyOwnObject>.

I don't understand how i adapt my data to fit in List<? extends Map<String, ?>> List<? extends Map<String, ?>> .

Thanks.

Answer 1

Okay. That <? extends Whatever> <? extends Whatever> is called a bounded wildcard . It will only match your ArrayList<YourObject> if YourObject belongs to a class implements Map<String, Something> , where Something can be any class (that one will match the unbounded wildcard ? ).

Your ArrayList is totally fine, since that implements the List interface. It's your custom MyOwnObject that needs to satisfy the above restrictions.

Read more about wildcards here .