如何用Stream将List的数据合并呢？

Question

你们好。请问如何将list的数据合并呢？

我想要的结果是相同月份和相同年份的数据合并 。
最终结果
List list = new ArrayList();
list.add(new Record( amount:166, month=12,year =2021,count=4))
list.add(new Record( amount:144, month=11,year =2021,count=4) )

Answer 1

public static void main(String[] args) {
        List<Record> list = new ArrayList<>();
        list.add(new Record(160.0, 12, 2021, 3));
        list.add(new Record(6.0, 12, 2021, 1));
        list.add(new Record(130.0, 11, 2021, 1));
        list.add(new Record(14.0, 11, 2021, 3));
        list = list.stream().collect(Collectors.toMap(r->r.getYear()+""+r.getMonth(), a -> a, (o1, o2) -> {
            o1.setAmount(o1.getAmount() + o2.getAmount());
            o1.setCount(o1.getCount() + o2.getCount());
            return o1;
        })).values().stream().collect(Collectors.toList());
        System.out.println(list);
    }


执行结果：
[Record{amount=166.0, month=12, year=2021, count=4}, Record{amount=144.0, month=11, year=2021, count=4}]