在Java 8中查找列表的最大值,最小值,总和和平均值
问题描述:
如何在Java 8中查找以下列表中的最大值,最小值,总和和平均值?在Java 8中查找列表的最大值,最小值,总和和平均值
List<Integer> primes = Arrays.asList(2, 3, 5, 7, 11, 13, 17, 19, 23, 29);
答
有一类的名字,IntSummaryStatistics
例如:
List<Integer> primes = Arrays.asList(2, 3, 5, 7, 11, 13, 17, 19, 23, 29);
IntSummaryStatistics stats = primes.stream()
.mapToInt((x) -> x)
.summaryStatistics();
System.out.println(stats);
输出:
IntSummaryStatistics{count=10, sum=129, min=2, average=12.900000, max=29}
希望它可以帮助
答
我认为了解问题的多个解决方案总是很好,可以选择最适合问题的权利。这里有一些其他的解决方案:
final List<Integer> primes = Arrays.asList(2, 3, 5, 7, 11, 13, 17, 19, 23, 29);
找出最大
// MAX -- Solution 1
primes.stream() //
.max(Comparator.comparing(i -> i)) //
.ifPresent(max -> System.out.println("Maximum found is " + max));
// MAX -- Solution 2
primes.stream() //
.max((i1, i2) -> Integer.compare(i1, i2)) //
.ifPresent(max -> System.out.println("Maximum found is " + max));
// MAX -- Solution 3
int max = Integer.MIN_VALUE;
for (int i : primes) {
max = (i > max) ? i : max;
}
if (max == Integer.MIN_VALUE) {
System.out.println("No result found");
} else {
System.out.println("Maximum found is " + max);
}
// MAX -- Solution 4
max = Collections.max(primes);
System.out.println("Maximum found is " + max);
找出最小
// MIN -- Solution 1
primes.stream() //
.min(Comparator.comparing(i -> i)) //
.ifPresent(min -> System.out.println("Minimum found is " + min));
// MIN -- Solution 2
primes.stream() //
.max(Comparator.comparing(i -> -i)) //
.ifPresent(min -> System.out.println("Minimum found is " + min));
// MIN -- Solution 3
int min = Integer.MAX_VALUE;
for (int i : primes) {
min = (i < min) ? i : min;
}
if (min == Integer.MAX_VALUE) {
System.out.println("No result found");
} else {
System.out.println("Minimum found is " + min);
}
// MIN -- Solution 4
min = Collections.min(primes);
System.out.println("Minimum found is " + min);
查找平均
// AVERAGE -- Solution 1
primes.stream() //
.mapToInt(i -> i) //
.average() //
.ifPresent(avg -> System.out.println("Average found is " + avg));
// AVERAGE -- Solution 2
int sum = 0;
for (int i : primes) {
sum+=i;
}
if(primes.isEmpty()){
System.out.println("List is empty");
} else {
System.out.println("Average found is " + sum/(float)primes.size());
}
查找总和
// SUM -- Solution 1
int sum1 = primes.stream() //
.mapToInt(i -> i) //
.sum(); //
System.out.println("Sum found is " + sum1);
// SUM -- Solution 2
int sum2 = 0;
for (int i : primes) {
sum2+=i;
}
System.out.println("Sum found is " + sum2);
但像consice越好,所以我最喜欢的是:
// Find a maximum with java.Collections
Collections.max(primes);
// Find a minimum with java.Collections
Collections.min(primes);
顺便说一句,甲骨文教程是一个金矿:https://docs.oracle.com/javase/tutorial/collections/streams/reduction.html
你可以通过编写一个应用程序来完成。你试过什么了? – BackSlash 2014-09-23 06:53:14
以下是您所需要的全部内容:http://docs.oracle.com/javase/8/docs/api/java/util/stream/Collectors.html – micha 2014-09-23 06:55:05
以下列表是什么?你打算发布一些代码吗? – 2014-09-23 06:55:44