1.對BigDecimal型別的值求和

List<Map<String,Object>> list = new ArrayList<>();
  Map<String,Object> stu1 = new HashMap<String, Object>();
  stu1.put("name", "衛莊");
  stu1.put("score", new BigDecimal(80));
  list.add(stu1);
  Map<String,Object> stu2 = new HashMap<String, Object>();
  stu2.put(
 
"name", "蓋聶");
  stu2.put("score", new BigDecimal(90));
  list.add(stu2);
  Map<String,Object> stu3 = new HashMap<String, Object>();
  stu3.put("name", "天明");
  stu3.put("score", new BigDecimal(60));
  list.add(stu3);
  BigDecimal sum = list.stream().map(x -> new BigDecimal(x.get("score").toString())).reduce(BigDecimal.ZERO,BigDecimal::add);
  System.out.println(
 
"三人總分："+sum);
  //結果：三人總分：230

2.對double型的值求和

List<Map<String,Object>> list = new ArrayList<>();
  Map<String,Object> stu1 = new HashMap<String, Object>();
  stu1.put("name", "衛莊");
  stu1.put("score", 80.0);
  list.add(stu1);
  Map<String,Object> stu2 = new HashMap<String, Object>();
  stu2.put(
 
"name", "蓋聶");
  stu2.put("score", 90.0);
  list.add(stu2);
  Map<String,Object> stu3 = new HashMap<String, Object>();
  stu3.put("name", "天明");
  stu3.put("score", 60.0);
  list.add(stu3);
  double sum = list.stream().collect(Collectors.summingDouble(x -> ((Double) x.get("score"))));
  System.out.println("三人總分："+sum);

//結果：三人總分：230