@Override
	public final boolean removeAll(Collection<?> c) {
        if (c == null) {
            throw new NullPointerException();
        }
        boolean hasChanged = false;
        for (Object o: c) {
            if (remove(o)) hasChanged = true;
        }
        return hasChanged;
    }
@ Override public final boolean removeAll ( Collection < ? > c ) { if ( c == null ) { throw new NullPointerException ( ) ; } boolean hasChanged = false ; for ( Object o : c ) { if ( remove ( o ) ) hasChanged = true ; } return hasChanged ; }
@see java.util.Set#removeAll(java.util.Collection)