Adding String to List<Integer>

Question

The result of the following code:

public class ListIntegerDemo1 {

    public static void addToList(List list) {list.add("0067");list.add("bb");}
    public static void main(String[] args) {
        List<Integer> list = new ArrayList<>();
        addToList(list);
        System.out.println(list.get(0));
    }     
}

is "0067".

I would have expected a RuntimeException or similar, as I'm adding a String to an Integer List.

Why is it working without any problem?

Answer 1

At run time, the generic type parameters are erased, so List<Integer> becomes List, and you can add any reference type to it.

If you change addToList(List list) to addToList(List<Integer> list), the compiler will prevent you from adding Strings to that list in this method.