NumberClassifier-JAVA8.ver

NumberClassifier.java

import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;

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(1, number + 1)
                .filter(potential -> number % potential == 0);
    }
    // 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;
    }

}