[英]Find maximum, minimum, sum and average of a list in Java 8
如何在Java 8中找到以下列表中数字的最大值,最小值,总和和平均值?
List<Integer> primes = Arrays.asList(2, 3, 5, 7, 11, 13, 17, 19, 23, 29);
有一个类名, 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}
希望能帮助到你
我认为知道一个问题的多个解决方案来选择最适合问题的解决方案总是好的。 以下是一些其他解决方案:
final List<Integer> primes = Arrays.asList(2, 3, 5, 7, 11, 13, 17, 19, 23, 29);
找到最大值
// 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);
找到最小值
// 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);
求平均值
// 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());
}
求和
// 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);
但要尽可能简洁,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,Oracle 教程是一个金矿: https : //docs.oracle.com/javase/tutorial/collections/streams/reduction.html
//By using lambda
int sum = primes.stream().mapToInt(a->a).sum();
System.out.println(sum);
int min = primes.stream().mapToInt(a->a).min().orElse(0);
System.out.println(min);
int max = primes.stream().mapToInt(a->a).max().orElse(0);
System.out.println(max);
double average = primes.stream().mapToInt(a->a).average().orElse(0);
System.out.println(average);
//By using Collections
System.out.println(Collections.min(primes));
System.out.println(Collections.max(primes));
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