ForEachPerformanceTest.java

package test;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * Created by sansword on 2017/1/28.
 */
public class ForEachPerformanceTest {
    public static void main(String[] args) {

        long differenceSum = 0;
        long maxDifference = 0;
        int sumSum = 0;
        int loopNum = 10000000;
        int maxIndex = -1;
        Integer[] differenceArray = new Integer[100];
        Arrays.fill(differenceArray, 0);
        for (int j = 0; j < loopNum; j++) {
            List<Integer> input = new ArrayList<>();
            for (int i = 0; i < 100; i++) {
                input.add((int) (1 + Math.random() * 100));
            }
            long startFor = System.currentTimeMillis();
            final int[] sumFor = {0};
            for (Integer integer : input) {
                sumFor[0] += integer;
            }
            long endFor = System.currentTimeMillis();

            long startForEach = System.currentTimeMillis();
            final int[] sumForEach = {0};
            input.forEach(integer -> sumForEach[0] += integer);
            long endForEach = System.currentTimeMillis();
            Long singleDifference = Math.abs((endForEach - startForEach) - (endFor - startFor));
            differenceSum += singleDifference;
            if (singleDifference > maxDifference) {
                maxDifference = singleDifference;
                maxIndex = j;
            }
            differenceArray[singleDifference.intValue()] += 1;
            sumSum += Math.abs(sumFor[0] - sumForEach[0]);
        }
        if (sumSum != 0) {
            throw new RuntimeException("something goes wrong.");
        }
        System.out.println("difference sum :" + differenceSum);
        System.out.println("Max difference:" + maxDifference + ", @" + maxIndex);
        System.out.println("difference avg. :" + ((differenceSum + 0.0) / loopNum));
        System.out.println("===== difference array =====");
        for (int i = 0; i < differenceArray.length; i++) {
            Integer currentDifference = differenceArray[i];
            if (currentDifference > 0) {
                System.out.println(i + ":" + currentDifference);
            }
        }

    }
}

Running result:

difference sum :3062
Max difference:47, @0
difference avg. :3.062E-4
===== difference array =====
0:9996984
1:3015
47:1

Process finished with exit code 0

It seems stream is slow when it's used for the first time (regardless of different or same object)
Then it'll be mostly the same.