Java lambda 循环累加求和

java 8 stream 提供了下面几种类型的求和

Stream::mapToInt
Stream::mapToDouble
Stream::mapToLong

	public void test() {
		List<Person> people = new ArrayList<>();
		people.add(new Person(\"zhangsan\",20));
		people.add(new Person(\"lisi\", 26));
		people.add(new Person(\"wangwu\",35));
		
		int sum = people.stream()
		          .mapToInt(p -> p.getAge())
		          .sum();
		System.out.println(\"Total of ages \" + sum);
	}

 但是没有BigDecimal类型，可以使用下面方法实现

	public static void test() {
		List<Person> list = new ArrayList<>();
		list.add(new Person(\"zhangsan\", 20, new BigDecimal(10.5)));
		list.add(new Person(\"lisi\", 26, new BigDecimal(22.2)));
		list.add(new Person(\"wangwu\", 35, new BigDecimal(15.54)));

		BigDecimal amounts = list.stream().map(item ->
                        item.getAmount())
                        .reduce(BigDecimal.ZERO,BigDecimal::add);
		amounts = amounts.setScale(1, BigDecimal.ROUND_UP);
		System.out.println(\"Total of amounts:\" + amounts);
	}