Java – generics and comparators

I was studying generics and found that the following code gave compile - time errors when comparing methods

class A<T> {
    String m1() {
        return null;
    }
}

class B {
    void test() {
        Comparator<A<String>> target = Comparator.comparing(A::m1).thenComparing(A::m1);
    }
}

Someone can help me understand this behavior; How can I solve this problem?

Solution

If the exact generic type is specified in the comparison method, the code is compiled

Comparator<A<String>> target =
    Comparator.<A<String>,String>comparing(A::m1).thenComparing(A::m1);