Most efficient way to make a copy of a large array in java

Question

I want to copy a large array of integer values say form array a to array b. I have found a couple of ways to do this, including:

int[] a = new int[]{1,2,3,4,5};
int[] b = new int[5];

System.arraycopy( a, 0, b, 0, a.length );

and

int[] a = new int[]{1,2,3,4,5};
int[] b = (int[])a.clone();

Since this is done on a mobile device i want to be able to do it most efficiently.

Please tell me the best way to do this.

Let's not forget Arrays.copyOf. http://stackoverflow.com/questions/12157300/clone-or-arrays-copyof — jdb, Feb 06 '13 at 07:39
@jdb it's risky - it's not available in earlier Android APIs, eg. API 8. — andr, Feb 06 '13 at 07:42

score 9 · Answer 1 · edited May 23 '17 at 11:51

9

System.arraycopy is better way.

Reason: Its implemented through native code so it's more efficient. Josh Bloch suggests (in Effective Java ) to avoid using clone() method to copy/clone an object.

Pls refer this : Effective Java: Analysis of the clone() method

edited May 23 '17 at 11:51

Community

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answered Feb 06 '13 at 07:30

rai.skumar

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@wojci apples and oranges - this is a comparison between `arraycopy()` and *naive* copying by looping over all the elements - this is not the same thing as `clone()`. – andr Feb 06 '13 at 07:40

score 2 · Answer 2 · answered Feb 06 '13 at 07:32

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System.arraycopy( a, 0, b, 0, a.length ); is a nice optimized function, if you build a new object, the execution will be slower..

answered Feb 06 '13 at 07:32

ƒernando Valle

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score 2 · Answer 3 · answered Feb 06 '13 at 07:36

Yeah, everybody's saying that arraycopy() is better, but most of people tend to forget that Dalvik VM is not Oracle VM and the sources they link to are referring to the Oracle VM. My guess is also that arraycopy() will be faster.

However

If you really, really need for this copy to most optimized, just time both methods and see how they perform. That is always the way to go if you really want to know the real answer. Do that especially on the devices you're targeting since it may be that it behaves drastically different from one device to another.

Evgeniy Dorofeev · Answer 4 · 2013-02-06T18:01:32.040

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I think this is the best way to make copies of arrays

int[] b = Arrays.copyOf(a, a.length);

edited Feb 06 '13 at 18:01

answered Feb 06 '13 at 07:42

Evgeniy Dorofeev

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just be aware that `Arrays.copyOf()` was added later to the API - it's not available in API 8 for example. – andr Feb 06 '13 at 07:44

Subhrajyoti Majumder · Answer 5 · 2013-02-06T07:57:26.320

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System.arraycopy is native implementation and efficient than cloning. It could copy array in single memorycopy(memcpy).

Find a article on wikipedia - java cloning disadvantage and alternative

edited Feb 06 '13 at 07:57

answered Feb 06 '13 at 07:31

Subhrajyoti Majumder

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Most efficient way to make a copy of a large array in java

5 Answers5