SingleResponsibilityPrinciple.java

package com.insightfullogic.java8.examples.chapter8;

import java.util.stream.IntStream;

public class SingleResponsibilityPrinciple {

    public static interface PrimeCounter {
        long countPrimes(int upTo);
    }

    public static class ImperativeSingleMethodPrimeCounter implements PrimeCounter {
        @Override
        // BEGIN imperative_single_method
public long countPrimes(int upTo) {
    long tally = 0;
    for (int i = 1; i < upTo; i++) {
        boolean isPrime = true;
        for (int j = 2; j < i; j++) {
            if (i % j == 0) {
                isPrime = false;
            }
        }
        if (isPrime) {
            tally++;
        }
    }
    return tally;
}
        // END imperative_single_method
    }

    public static class ImperativeRefactoredPrimeCounter implements PrimeCounter {
        @Override
        // BEGIN imperative_refactored
public long countPrimes(int upTo) {
    long tally = 0;
    for (int i = 1; i < upTo; i++) {
        if (isPrime(i)) {
            tally++;
        }
    }
    return tally;
}

private boolean isPrime(int number) {
    for (int i = 2; i < number; i++) {
        if (number % i == 0) {
            return false;
        }
    }
    return true;
}
        // END imperative_refactored
    }

    public static class FunctionalPrimeCounter implements PrimeCounter {

        @Override
        // BEGIN functional
public long countPrimes(int upTo) {
    return IntStream.range(1, upTo)
                    .filter(this::isPrime)
                    .count();
}

private boolean isPrime(int number) {
    return IntStream.range(2, number)
                    .allMatch(x -> (number % x) != 0);
}
        // END functional
    }

    public static class ParallelFunctionalPrimeCounter implements PrimeCounter {
        @Override
        // BEGIN parallel_functional
public long countPrimes(int upTo) {
    return IntStream.range(1, upTo)
                    .parallel()
                    .filter(this::isPrime)
                    .count();
}

private boolean isPrime(int number) {
    return IntStream.range(2, number)
            .allMatch(x -> (number % x) != 0);
}
        // END parallel_functional
    }

}