StreamとパラレルStreamの比較

Sum.java

import java.util.function.IntConsumer;
import java.util.stream.IntStream;

public class Sum {

    private static final int SIZE = 1_000_000;

    public Sum() {
        evaluate("sum000", i -> sum000());
        evaluate("sum001", i -> sum001());
        evaluate("sum002", i -> sum002());
    }

    private void evaluate(String prefix, IntConsumer consumer) {
        IntStream.range(0, 20)
                .forEach(consumer);

        long start = System.nanoTime();
        IntStream.range(0, 100)
                .forEach(consumer);
        long end = System.nanoTime();

        result(prefix, end - start);
    }

    private IntStream createIntStream() {
        return IntStream.range(1, SIZE);
    }

    private int sum000() {
        int sum = 0;
        for (int i = 0; i <= SIZE; i++) {
            sum += i;
        }

        return sum;
    }

    private int sum001() {
        return createIntStream().sum();
    }

    private int sum002() {
        return createIntStream().parallel().sum();
    }

    private void result(String prefix, long time) {
        System.out.println(prefix + ": elapsed=" + time / 1_000);
    }

    public static void main(String[] args) {
        System.out.println("os.arch=" + System.getProperty("os.arch"));
        System.out.println("os.name=" + System.getProperty("os.name"));
        System.out.println("os.version=" + System.getProperty("os.version"));
        System.out.println("java.version=" + System.getProperty("java.version"));
        System.out.println("java.vm.info=" + System.getProperty("java.vm.info"));
        System.out.println("java.vm.name=" + System.getProperty("java.vm.name"));
        System.out.println("sun.management.compiler=" + System.getProperty("sun.management.compiler"));
        System.out.println("poolParallelism=" + java.util.concurrent.ForkJoinPool.getCommonPoolParallelism());

        new Sum();
    }
}