技術標籤：Javalambdastream

根據性別進行彙總，求男女的年齡總和

public static void main(String[] args) {

        List<Map<String,String>> arrayList = new ArrayList<>();

        Map<String, String> map1 = new HashMap<>();
        map1.put("gender","女");
        map1.put
 
("age","13");
        arrayList.add(map1);
        Map<String, String> map2 = new HashMap<>();
        map2.put("gender","女");
        map2.put("age","11");
        arrayList.add(map2);
        Map<String, String> map3 = new
 
 HashMap<>();
        map3.put("gender","男");
        map3.put("age","15");
        arrayList.add(map3);
        Map<String, String> map4 = new HashMap<>();
        map4.put("gender","男");
        map4.put("age",
 
"11");
        arrayList.add(map4);
		//方法1
        Map<String, DoubleSummaryStatistics> collect = arrayList.stream()
                .collect(Collectors.groupingBy(e -> e.get("gender"),
         Collectors.summarizingDouble(e -> Double.valueOf(e.get("age")))));

        double v1 = collect.get("男").getSum();
        double v2 = collect.get("女").getSum();
        System.out.println("男性年齡總和：" + v1 + "女性年齡總和：" + v2);

		//方法2
        Map<String, List<Map<String, String>>> list = arrayList.stream().collect(Collectors.groupingBy(g -> g.get("gender")));
        list.forEach((k,vlist)->{
            DoubleSummaryStatistics sum = vlist.stream().collect(Collectors.summarizingDouble(e->Double.valueOf(e.get("age"))));
            System.out.println(k + "性年齡總和：" + sum.getSum());
        });
    }