Java流API : How to use method reference?

Question

有代码

     class Person {
        private ZonedDateTime date ;
        private int regionId;
        private int centerId;
        private int amount1;
        private float percent1;
}

 List<Person> entityList = new ArrayList<>();

我按年月分组，如下所示:

  listPerson.stream()
            .collect(Collectors.groupingBy(i -> i.getDate().getMonth(),Collectors.collectingAndThen(Collectors.toList(),
            l -> {
                   Integer sumAmount1 = l.stream().collect(Collectors.summingInt(i -> i.getAmount1()));                                                 
                   Double avgPerc1 = l.stream().collect(Collectors.averagingDouble(i -> i.getPercent1()));                                                   
                   List<String> data = new ArrayList<>();
                   data.add(Integer.toString(sumAmount1));
                   data.add(Double.toString(avgPerc1));                                                   
                   return data;
                }
            ))).forEach((k,v) -> System.out.println(k.getValue() + "-" + v.toString()));

我还以相同的方式按年份、regionId、centerId 进行分组:

 listPerson.stream()
                .collect(Collectors.groupingBy(i -> i.getDate().getYear(),Collectors ......

但是我有很多重复的代码，其中部分与

l -> {...} 

重复了很多次。如何使用方法引用代替 l -> {...}？

Answer 1

IntelliJ 确实可以为您做到这一点。您甚至不必考虑它。

提示的键盘快捷键(黄色)是AltEnter

这就是我最终得到的结果

public static void main(String[] args)
{
    List<Person> listPerson = null;        

    listPerson.stream()
        .collect(Collectors.groupingBy(i -> i.getDate().getMonth(), Collectors.collectingAndThen(Collectors.toList(),
            Scratch::apply
    )))
    .forEach((k,v) -> System.out.println(k.getValue() + "-" + v.toString()));
}

private static List<String> apply(List<Person> l)
{
    int sumAmount1 = l.stream().mapToInt(Person::getAmount1).sum();
    Double avgPerc1 = l.stream().collect(Collectors.averagingDouble(Person::getPercent1));
    List<String> data = new ArrayList<>();
    data.add(Integer.toString(sumAmount1));
    data.add(Double.toString(avgPerc1));
    return data;
}