public CopyOnWriteArraySet(Collection<? extends E> c){
  al=new CopyOnWriteArrayList<E>();
  al.addAllAbsent(c);
}

public CopyOnWriteArraySet ( Collection < ? extends E > c ) { al = new CopyOnWriteArrayList < E > ( ) ; al . addAllAbsent ( c ) ; }
creates a set containing all of the elements of the specified collection .
