stream的优化：java封装的拆箱与装箱的弊端

authors.stream()
    .map(author->author.getAge)
    .map(age->age+10)//Stream<Integer>
    .filter(age>18)//Stream<Integer>
    .foreach(System.out::println);

authors.stream()
    .mapToInt(author->author.getAge)
    .map(age->age+10)//IntStream
    .filter(age>18)//IntStream
    .foreach(System.out::println);