Java lambda 循环累加求和代码
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);
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