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 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_DOWN); System.out.println("Total of amounts:" + amounts); // 或者 BigDecimal sum = list .stream() .map(Person::getAmount) .reduce(BigDecimal::add) .get(); sum = sum.setScale(1, BigDecimal.ROUND_DOWN); System.out.println("Total of sums: " + sum); }

补充知识：Java算法——求1到100累加的和，3种循环

1、for循环

int sum = 0;for (int i = 1; i <= 100; i++) {sum += i;}System.out.println("1到100累加的和为：" + sum);

2、while循环

int sum = 0;int i = 1;while (i <= 100) {sum += i;i++;}System.out.println("1到100累加的和为：" + sum);

3、do...while循环

int sum = 0;int i = 1;do {sum += i;i++;} while (i <= 100);System.out.println("1到100累加的和为：" + sum);

以上这篇Java lambda 循环累加求和代码就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持。