Unable to add object to generic list using wildcard [duplicate]

问题

This question already has answers here:

Can't add value to the Java collection with wildcard generic type (4 answers)

Closed 5 years ago.

Why can't I add any object here , I was hoping I would be allowed to add any kind of object in such a list.

List<?> l = new ArrayList<Object>();
l.add(new Object());
l.add(new String("hello"));

回答1:

Why not just:

    List<Object> l = new ArrayList<>();
    l.add(new Object());
    l.add(new String("hello"));

来源：https://stackoverflow.com/questions/24756464/unable-to-add-object-to-generic-list-using-wildcard