I gave List<?> as a simple example; usually we're talking about List<? extends Foo> or similar. Anything that involves a ? anywhere is an existential type, and they're the only way to write a whole lot of things safely, e.g. any kind of callback has to involve a "? super" type to avoid disallowing perfectly valid code. Unless the Java community has abandoned generics and decided to go back to using casts everywhere there's really no alternative in the language.