code: public boolean addAll(Collection<? extends Character> c) {
          boolean retVal = false;
          final Iterator<? extends Character> i = c.iterator();
          int n = c.size();
          while (n-- != 0)
              if (add(i.next())) retVal = true;
          return retVal;
      }
docs: Adds all elements of the given collection to this collection.
  
  @param c a collection.
  @return <code>true</code> if this collection changed as a result of the call.