Question

I declare the private variable as

private List<MultipartFile> files;

When I want initialize it I do in this way:

files=new ArrayList<CommonsMultipartFile>();

you can see the CommonsMultipartFile extends the MultipartFile Interface
The compile give me error as:

Type mismatch: cannot convert from ArrayList<CommonsMultipartFile> to List<MultipartFile>

Anyone who know the reason?
If I really want to Stable the collection and inside class type, how can I do it?
Can I do similar staff in C++?

Answer 1

If im not mistaken, in java generics :

If you have two class A, class B extends A and a generic class Generic<T>, then Generic<B> does not extends Generic<A>. That’s why your cast does not work.

You could declare files as :

private List<? extends MultipartFiles> files;

With this, you should be able to do your assignment.

Edit : As it’s said in other response, this declaration would prevent to add other things than null. Limited interest indeed…