Kotlin 按性别列出的成员名单名称
示例
//Java: Map<Person.Sex, List<String>> namesByGender = roster.stream().collect( Collectors.groupingBy( Person::getGender, Collectors.mapping( Person::getName, Collectors.toList())));
//科特林: val namesByGender =roster.groupBy{it.gender}.mapValues { it.value.map {it.name} }