Java lambda 循环累加求和代码

时间:2021-07-24 22:00:11

java 8 stream 提供了下面几种类型的求和

Stream::mapToInt

Stream::mapToDouble

Stream::mapToLong

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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

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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

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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

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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

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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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原文链接:https://blog.csdn.net/angus_Lucky/article/details/85062728