Java - for, for-each and forEach performance test

In this article, I would like to show results from simple performance tests for different types of for loop made on int array in Java.

Tests show what loop type is faster in different cases.

Below test conclusions:

• for loop is fastest in many cases,
• time necessary to iterate over array using different for-s going to be similar when array sizes are bigger,
• in some cases for-each can be faster, what is visible when array sizes are bigger (for small arrays it is visible mostly).

Used Java: Amazon Corretto, x64, JDK 1.8.0_292

Used OS: Windows 10 x64

Used PC:

• Ryzen 9 5900x
• DRR 4 (2x 32GB)
• Samsung SSD M.2 970 EVO (1TB)
• GeForce GTX 970 (4GB RAM)

Total times needed to iterate over the array:

Used source code:

import com.google.common.base.Stopwatch;

import java.util.Arrays;
import java.util.function.IntConsumer;

public class Example {

    public static void main(String[] args) {

        int size = 1_000_000; // change it to your size

        int[] array = new int[size];
        for (int i = 0; i < array.length; i++) {
            array[i] = i;
        }

        // for loop
        {
            int sum = 0;

            Stopwatch stopwatch = Stopwatch.createStarted();
            for (int i = 0; i < array.length; i++) {
                sum += array[i];
            }
            System.out.println(sum + " in " + stopwatch.stop());
        }

        // for-each loop
        {
            int sum = 0;

            Stopwatch stopwatch = Stopwatch.createStarted();
            for (int value : array) {
                sum += value;
            }
            System.out.println(sum + " in " + stopwatch.stop());
        }

        // forEach method with stream
        {
            IntSumator sumator = new IntSumator();

            Stopwatch stopwatch = Stopwatch.createStarted();
            Arrays.stream(array).forEach(sumator); // or just Arrays.stream(array).forEach(value -> { ... });
            System.out.println(sumator.getSum() + " in " + stopwatch.stop());
        }
    }

    private static class IntSumator implements IntConsumer {

        private int sum = 0;

        public int getSum() {
            return this.sum;
        }

        @Override
        public void accept(int value) {
            this.sum += value;
        }
    }
}

 Stopwatch class from:

<!-- https://mvnrepository.com/artifact/com.google.guava/guava -->
<dependency>
  <groupId>com.google.guava</groupId>
  <artifactId>guava</artifactId>
  <version>27.0.1-jre</version>
</dependency>

Alternative test source code

Alternatively, we can use the following test that repeats same tests few times dividing time by tests amount:

import com.google.common.base.Stopwatch;

import java.util.Arrays;
import java.util.concurrent.TimeUnit;
import java.util.function.IntConsumer;

public class Example {

    public static void main(String[] args) throws InterruptedException {

        int repeatsCount = 1000;
        int arraySize = 1_000_000;

        TimeUnit resultUnit = TimeUnit.MICROSECONDS;

        int[] array = new int[arraySize];
        for (int i = 0; i < array.length; i++) {
            array[i] = i;
        }

        int sum1 = 0;
        int sum2 = 0;
        IntSumator sumator3 = new IntSumator();

        Stopwatch stopwatch1 = Stopwatch.createUnstarted();
        Stopwatch stopwatch2 = Stopwatch.createUnstarted();
        Stopwatch stopwatch3 = Stopwatch.createUnstarted();

        for (int j = 0; j < repeatsCount; ++j) {

            // for loop

            stopwatch1.start();
            for (int i = 0; i < array.length; i++) {
                sum1 += array[i];
            }
            stopwatch1.stop();

            // for-each loop

            stopwatch2.start();
            for (int value : array) {
                sum2 += value;
            }
            stopwatch2.stop();

            // forEach method with stream

            stopwatch3.start();
            Arrays.stream(array).forEach(sumator3); // or just Arrays.stream(array).forEach(value -> { ... });
            stopwatch3.stop();
        }

        int sum3 = sumator3.getSum();

        double time1 = (double)stopwatch1.elapsed(resultUnit) / repeatsCount;
        double time2 = (double)stopwatch2.elapsed(resultUnit) / repeatsCount;
        double time3 = (double)stopwatch3.elapsed(resultUnit) / repeatsCount;

        String unitAbbreviation = renderUnit(resultUnit);

        System.out.println("time: " + time1 + " " + unitAbbreviation + ", sum: " + sum1 + " - for loop");
        System.out.println("time: " + time2 + " " + unitAbbreviation + ", sum: " + sum2 + " - for-each loop");
        System.out.println("time: " + time3 + " " + unitAbbreviation + ", sum: " + sum3 + " - forEach method with stream");
    }

    private static class IntSumatorimplements IntConsumer {

        private int sum = 0;

        public int getSum() {
            return this.sum;
        }

        @Override
        public void accept(int value) {
            this.sum += value;
        }
    }

    private static String renderUnit(TimeUnit unit) {

        switch (unit) {
            case NANOSECONDS:  return "ns";
            case MICROSECONDS: return "\u03bcs"; // μs
            case MILLISECONDS: return "ms";
            case SECONDS:      return "s";
            case MINUTES:      return "min";
            case HOURS:        return "h";
            case DAYS:         return "d";
            default:
                throw new AssertionError();
        }
    }
}

See also

1. Java - iterate over array of strings