Question

When I write the following code compiler says that

cannot convert from ArrayList<String> to List<Comparable>

private List<Comparable> get(){
    return new ArrayList<String>();
}

But when I write return type with wildcard, the code compiles.

private List<? extends Comparable> get() {
    return new ArrayList<String>();
}

Can somebody explain me why?

Answer 1

A List<String> is not a List<Comparable>.
After all, you can put an Integer into a List<Comparable>.