Use java8 summing array of stream

1. summing the values ​​of type BigDecimal

  List<Map<String,Object>> list = new ArrayList<>();
  Map<String,Object> stu1 = new HashMap<String, Object>();
  stu1.put("name", "卫庄");
  stu1.put("score", new BigDecimal(80));
  list.add(stu1);
  Map<String,Object> stu2 = new HashMap<String, Object>();
  stu2.put("name", "盖聂");
  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("三人总分："+sum);

// result: three score: 230

2. The value of the sum of the double type

List<Map<String,Object>> list = new ArrayList<>();
  Map<String,Object> stu1 = new HashMap<String, Object>();
  stu1.put("name", "卫庄");
  stu1.put("score", 80.0);
  list.add(stu1);
  Map<String,Object> stu2 = new HashMap<String, Object>();
  stu2.put("name", "盖聂");
  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 ( "three score:" + sum);

// result: three score: 230