关于list.stream().map(User::getUserId).collect(Collectors.toList())的写法

今天看同事的代码，见到下面这一段，没看懂，去网上百度了一下，才明白是什么意思

List<User> UserList = userMapper.selectAllUser();
List<String> userIdList = UserList.stream().map(User::getUserId).collect(Collectors.toList());

等价于

List<User> UserList = userMapper.selectAllUser();
List<String> userIdList = new ArrayList<>();
for(User user : UserList){
     
	userIdList.add(user.getUserId());
}