Question

I have an interface DataSeries with a method

int[] getRawData();

For various reasons (primarily because I’m using this with MATLAB, and MATLAB handles int[] well) I need to return an array rather than a List.

I don’t want my implementing classes to return the int[] array because it is mutable. What is the most efficient way to copy an int[] array (sizes in the 1000-1000000 length range) ? Is it clone()?

Answer 1

The only alternative is Arrays#copyOf() (which uses System#arrayCopy() under the hoods).

Just test it.

package com.stackoverflow.q2830456;

import java.util.Arrays;
import java.util.Random;

public class Test {

    public static void main(String[] args) throws Exception {
        Random random = new Random();
        int[] ints = new int[100000];
        for (int i = 0; i < ints.length; ints[i++] = random.nextInt());

        long st = System.currentTimeMillis();
        test1(ints);
        System.out.println(System.currentTimeMillis() - st);

        st = System.currentTimeMillis();
        test2(ints);
        System.out.println(System.currentTimeMillis() - st);
    }

    static void test1(int[] ints) {
        for (int i = 0; i < ints.length; i++) {
            ints.clone();
        }
    }

    static void test2(int[] ints) {
        for (int i = 0; i < ints.length; i++) {
            Arrays.copyOf(ints, ints.length);
        }
    }

}

20203
20131

and when test1() and test2() are swapped:

20157
20275

The difference is negligible. I’d say, just go for clone() since that is better readable and Arrays#copyOf() is Java 6 only.

_{Note: actual results may depend on platform and JVM used, this was tested at an Dell Latitude E5500 with Intel P8400, 4GB PC2-6400 RAM, WinXP, JDK 1.6.0_17_b04}