JAVA : Set addAll() vs adding using loop

Question

I was trying to add Integers from 2 sets into single Set via for loop and also using addAll() method provided by Collections. For test purpose, I have populated 2 Sets with

Answer 1

Concerning your question about how it is handled internally, just check the available source code, e.g. Ctrl-click in eclipse and find the implementation, which in your case is in AbstractCollection:

    public boolean addAll(Collection c) {
      boolean modified = false;
      for (E e : c)
        if (add(e))
            modified = true;
      return modified;
    }

(from JDK 1.7)