import java.util.ArrayList;
import java.util.List;
public class Numbers {
    public static void main(String[] args) {
        List<Number> lst = new ArrayList<>();
        lst.add(1);
        lst.add(2.0);
        for (Number n : lst) System.out.println(n.getClass() + " : " + n);
    }
}

interface MaList1<E> extends List<E> { }
interface MaList2<E,T> extends List<E> { }
interface MaList3 extends List<Integer> { }