Java lambda 循环累加求和代码

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 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()

.mapTohttp://Int(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 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YUOJNl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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