block6.java

public static void printList(List<? extends Number> numList) {
    for (Number n : numList) {
        System.out.println(n);
    }
}

List<Integer> integerList = new ArrayList<>(Arrays.asList(1, 2, 3));
List<Double> doubleList = new ArrayList<>(Arrays.asList(1.1, 2.2, 3.3));
printList(integerList); // 1, 2, 3
printList(doubleList); // 1.1, 2.2, 3.3