Can I add to a generic collection of type A values of type B ,which extends A, without any special syntax?

Question

public class Stack {
    public Stack () {....}
    public void push (E e) {....}
    public E pop () {....}
    public boolean isEmpty(){....}
}

public void p         


        

Answer 1

Your code specified that it only accepts a Collection with the same type parameter as the Stack has.

You should write the pushAll method like this:

public void pushAll (Collection src)

This means that you expect a Collection of some type that extends E (i.e. you don't care what specific type it is, but it must be E or some sub-type of it).

Look at the definition of Collection.addAll(): it's defined in the same way.