Java8新特性——lambda表达式.（案例：完全数分类）

需求:输入一个数,判断其类型(完全数,过剩数,不足数)

完全数:自身之外所有因数和==自身

过剩数:自身之外所有因数和>自身

不足数:自身之外所有因数和<自身

 package cn._3.numberclassifier;

 //BEGIN number_classifier_java8
 import java.util.List;
 import java.util.stream.IntStream;

 import static java.lang.Math.sqrt;
 import static java.util.stream.Collectors.toList;
 import static java.util.stream.IntStream.range;

 public class NumberClassifier {

     // BEGIN java8_filter
     public static IntStream factorsOf(int number) {
         return range(, number + ).filter(potential -> number % potential == );
     }
     // END java8_filter
     public static int aliquotSum(int number) {
         return factorsOf(number).sum() - number;
     }
     public static boolean isPerfect(int number) {
         return aliquotSum(number) == number;
     }
     public static boolean isAbundant(int number) {
         return aliquotSum(number) > number;
     }
     public static boolean isDeficient(int number) {
         return aliquotSum(number) < number;
     }
     // END number_classifier_java8

     // BEGIN java8_filter_fast
     public static List<Integer> fastFactorsOf(int number) {
         List<Integer> factors = range(, (int) (sqrt(number) + ))
                 .filter(potential -> number % potential == ).boxed()// 返回stream<Integer>
                 .collect(toList());// 折叠/化约,reduce
         List<Integer> factorsAboveSqrt = factors.stream().map(e -> number / e).collect(toList());
         factors.addAll(factorsAboveSqrt);
         //将stream变为ArrayList
         return factors.stream().distinct().collect(toList());
     }
     // END java8_filter_fast
 }

测试类:

 package cn._3.numberclassifier;

 public class Mmain {

     public static void main(String[] args) {
         Integer number = ;
         System.out.println(NumberClassifier.isPerfect(number)+","+NumberClassifier.isAbundant(number)+","+NumberClassifier.isDeficient(number));
     }
 }