stream流求和

List<Vo> list = new ArrayList<>();
for (int i = 0; i < 4; i++) {
    Vo vo = new Vo();
    vo.setName("21");
    vo.setGrade(new Double(2 + i));
    list.add(vo);
}
double sum = list.stream().mapToDouble(Vo -> {
    Double grade = Vo.getGrade();
    return grade;
}).sum();
System.out.println(sum);

private static void reduce() {
   //使用reduce聚合函数，实现累加器
   BigDecimal reduce = list.stream().filter(obj -> obj.getMoney() != null).map(User::getMoney).reduce(BigDecimal.ZERO, BigDecimal::add);
   System.out.println("BigDecimal求和"+reduce);
}

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