list 转map,计算相同key值下对象数量的和

1，将list通过某个字段转为map 2，计算相同key中对象中数量的和

public static void main(String[] args) {
          
   
        ArrayList<TypeSourceVo> personList = new ArrayList<>();
        TypeSourceVo vo1 = new TypeSourceVo();
        TypeSourceVo vo2 = new TypeSourceVo();
        TypeSourceVo vo3 = new TypeSourceVo();
        vo1.setType("qd");
        vo2.setType("qd");
        vo3.setType("qhiuiuew");
        vo1.setNum(32);
        vo3.setNum(25);
        vo2.setNum(62);
        personList.add(vo1);
        personList.add(vo2);
        personList.add(vo3);
        // 求集合中对象的年龄的总和
        Optional<Integer> reduce3 = personList.stream().map(p -> p.getNum()).reduce(Integer::sum);
        System.out.println(reduce3);  //Optional[50]
		//记录另一种方式
		 //Map<String, List<String>> map = vos.stream().collect(
         //           Collectors.groupingBy(
         //                   DisposalVo::getStreetName, Collectors.mapping(
         //                          DisposalVo::getStatus, Collectors.toList())));
        Map<String, List<TypeSourceVo>> collect = personList.stream().collect(Collectors.groupingBy(TypeSourceVo::getType));
        for (Map.Entry<String, List<TypeSourceVo>> entry : collect.entrySet()) {
          
   
            System.out.println(entry.getKey() + "------" + entry.getValue());
            String key = entry.getKey();
            Optional<Integer> reduce = entry.getValue().stream().map(vo -> vo.getNum()).reduce(Integer::sum);

            System.out.println("type为："+key+",数量为："+reduce);
        }
    }