What is the difference between overloading methods with varargs and methods with single arguments in Java?

Question

Consider given example:

class Create {
    Create(int num) {}
    Create(Integer num) {}
    public static void test(int... a) { }
    public static void test(Integer... a) { }

    public static void main(String[] args) {
        new Create(1); // ok
        Create.test(1); // error: reference to test is ambiguous
    }
}

Can someone explain me what is the difference for compiler in these two cases?