Question

The following method generates a warning, but it looks safe to me. I’m sure the problem is with me:

public <S extends CharSequence> S foo(S s) {
    return (S) new StringBuilder(s);
}

It looks like this will always return the argument s. Can anyone show an example that would cause this method to throw an exception?

Edit: I’m not particularly interested in the question of whether generics are necessary here. Rather, I’m looking for a demonstration of how this method is unsafe.

Answer 1

foo(“test”);

is enough to make java try to cast a StringBuilder in a String.

Your code is guaranteed o be wrong, can you explain what you’re trying to achieve plase ?