Loop VS System.arraycopy

Everyone feels the need to copy arrays around in java. So whats the best option to use?

1. Using a simple for loop to iterate and copy the content of each element over to the other element.
2. Using System.arraycopy to copy over the contents

Lets have a faceoff of these two methods and get the numbers out to prove the point. Here is the benchmarking code I wrote to get the numbers.

public class ArrayCopy {
public static final int ITERATION_AMOUNT = 150000;

public static void main(String[] args) {
int testSizes[] = { 10, 100, 1000, 10000, 100000, 1000000 };
for (int i = 0; i < testSizes.length; i++) performTest(testSizes[i]); } public static void performTest(int size) { int[] sourceArray; int[] destArray; long startTime; long endTime; System.out.println("Testing array copy vs. for loop with " + size + " elements..."); sourceArray = new int[size]; destArray = new int[size]; // Fill the source array with garbage for (int i = 0; i < size; i++) sourceArray[i] = i; /////////////////// System.arraycopy test ////////////////// // Time to initialise the timers startTime = System.currentTimeMillis(); for (int i = 0; i < ITERATION_AMOUNT; i++) System.arraycopy(sourceArray, 0, destArray, 0, size); endTime = System.currentTimeMillis(); System.out.println("Copying with System.arraycopy took " + (endTime - startTime) + " ms."); /////////////////////// For loop test ////////////////////// // Time to initialise the timers startTime = System.currentTimeMillis(); for (int i = 0; i < ITERATION_AMOUNT; i++) for (int j = 0; j < size; j++) destArray[j] = sourceArray[j]; endTime = System.currentTimeMillis(); System.out.println("Copying with for loop took " + (endTime - startTime) + " ms.\n\n"); } }[/sourcecode] And here are the results… Testing array copy vs. for loop with 10 elements…
Copying with System.arraycopy took 15 ms.
Copying with for loop took 16 ms.

Testing array copy vs. for loop with 100 elements…
Copying with System.arraycopy took 15 ms.
Copying with for loop took 79 ms.

Testing array copy vs. for loop with 1000 elements…
Copying with System.arraycopy took 187 ms.
Copying with for loop took 625 ms.

Testing array copy vs. for loop with 10000 elements…
Copying with System.arraycopy took 2156 ms.
Copying with for loop took 4625 ms.

I managed to generate a chart to display the results graphiacally.

Since System.arraycopy is a native method it is going to be the faster than the looping approach. I think this should be enough to convince our CTO that System.arraycopy is indeed faster than the looping approach that he seems to utilize in one of the most critical sections of code assuming that he is writing the fastest piece of code.

Tags: Java, Performance