Java Collections using wildcard

Answer 1

The point of bounded wildcard types is their use in method signatures to increase API flexibility. If, for example, you implement a generic Stack, you could provide a method to push a number of elements to the stack like so:

public void pushAll(Iterable elements) {
    for(E element : elements){
       push(e);
    }
}

Compared to a pushAll(Iterable elements) signature without a wildcard, this has the advantage that it allows collections of subtypes of E to be passed to the method - normally that would not be allowed because an Iterable is, somewhat counterintuitively, not a subclass of Iterable