code: public boolean containsAll(Collection<?> c) {
          return (c instanceof Set)
              ? compareSets(al.getArray(), (Set<?>) c) >= 0
              : al.containsAll(c);
      }
docs: Returns {@code true} if this set contains all of the elements of the
  specified collection.  If the specified collection is also a set, this
  method returns {@code true} if it is a <i>subset</i> of this set.
  
  @param  c collection to be checked for containment in this set
  @return {@code true} if this set contains all of the elements of the
  specified collection
  @throws NullPointerException if the specified collection is null
  @see #contains(Object)