Question

I have the following problem when using java generic. Basically I need to do a conversion from an list of subtype to a list of its supertype, and I defines a method like this:

public static <T> List<T> getList(List<? extends T> input) {
    ArrayList<T> list = new ArrayList<T>();
    list.addAll(input);
    return list;
}

However I’m not sure how I can invoke this method? Given type A, B extends A:

List<A> alist = getList(List<B> blist);

has a mismatch type, because in this case I only supply B’s type information to the method invocation.

How can I invoke the method with the type information A supplied?

Thanks.

Answer 1

List<B> blist = ...
List<A> alist = ClassName.<A>getList(blist);

Note that you could also just use ArrayList‘s constructor here:

List<A> alist = new ArrayList<A>(blist);