û kotlin collections EmptySet Set Nothing io Serializable serialVersionUID Long size Int contains Boolean element containsAll elements Collection equals other Any hashCode isEmpty iterator Iterator readResolve toString Stringh                ¸ "ÂÀBJ  2 (8H–J 2(8HJ 2(8H–J8HJ8HJ8H–J8 HJ8 HRHX‚Tº è‹¿í®…ØÆ^R  8VHX–ò: 0 0 0 0 0 0 0 0 0 0 0