java中数组多种遍历求和的效率分析

int型数组的遍历求和效率分析

转换成流的形式，再求和。IntStream.of(a).sum();
另一种转换流求和的方式，Arrays.stream(a).sum();
普通for loop 求和：for i
增强for loop 求和：for-each

测试方法使用的是 System.nanoTime() 求出求和段的运行时间，单位为纳秒(10^-9 s)

测试代码如下：

class Solution {
    public static void main(String[] args) {
        int[] a = new int[100];
        for (int i = 0; i < 100; i++) {
            a[i] = i + 1;
        }
        long l1, l2;
        int sum1, sum2, sum3 = 0, sum4 = 0;

        l1 = System.nanoTime();
        sum1 = IntStream.of(a).sum();
        l2 = System.nanoTime();
        System.out.print("IntStream.of(a).sum(): ");
        System.out.println(sum1);
        System.out.println(l2 - l1);

        l1 = System.nanoTime();
        sum2 = Arrays.stream(a).sum();
        l2 = System.nanoTime();
        System.out.print("Arrays.stream(a).sum(): ");
        System.out.println(sum2);
        System.out.println(l2 - l1);

        l1 = System.nanoTime();
        for (int i = 0; i < a.length; i++) {
            sum3 += a[i];
        }
        l2 = System.nanoTime();
        System.out.print("for loop: ");
        System.out.println(sum3);
        System.out.println(l2 - l1);

        l1 = System.nanoTime();
        for (int i : a) {
            sum4 += i;
        }
        l2 = System.nanoTime();
        System.out.print("iterator loop: ");
        System.out.println(sum4);
        System.out.println(l2 - l1);
    }
}