マルチコアプロセッサを活用して Java のパフォーマンスを向上させるにはどうすればよいでしょうか?

public class SumArraySerial {

    public static int sumArray(int[] arr) {
        int sum = 0;
        for (int i : arr) {
            sum += i;
        }
        return sum;
    }

}

import java.util.concurrent.ForkJoinPool;
import java.util.stream.IntStream;

public class SumArrayParallel {

    public static int sumArray(int[] arr) {
        return IntStream.of(arr).parallel().sum();
    }

    public static int sumArrayForkJoin(int[] arr) {
        ForkJoinPool pool = ForkJoinPool.commonPool();
        return pool.invoke(new SumArrayTask(arr, 0, arr.length));
    }

    private static class SumArrayTask extends RecursiveTask<Integer> {

        private int[] arr;
        private int start;
        private int end;

        public SumArrayTask(int[] arr, int start, int end) {
            this.arr = arr;
            this.start = start;
            this.end = end;
        }

        @Override
        protected Integer compute() {
            int sum = 0;
            if ((end - start) <= 10000) { // 阈值，执行串行计算
                for (int i = start; i < end; i++) {
                    sum += arr[i];
                }
            } else { // 超出阈值，分解任务和并行计算
                int mid = (start + end) / 2;
                SumArrayTask left = new SumArrayTask(arr, start, mid);
                SumArrayTask right = new SumArrayTask(arr, mid, end);
                left.fork();
                right.fork();
                sum = left.join() + right.join();
            }
            return sum;
        }
    }

}