How to create a sub array from another array in Java?

Question

How to create a sub-array from another array? Is there a method that takes the indexes from the first array such as:

methodName(object array, int start, int end)

I don't want to go over making loops and making my program suffer.

I keep getting error:

cannot find symbol method copyOfRange(int[],int,int)

This is my code:

import java.util.*;

public class testing 
{
    public static void main(String [] arg) 
    {   
        int[] src = new int[] {1, 2, 3, 4, 5}; 
        int b1[] = Arrays.copyOfRange(src, 0, 2);
    }
}

score 397 · Answer 1 · edited Jan 07 '17 at 10:43

397

You can use

JDK > 1.5

Arrays.copyOfRange(Object[] src, int from, int to)

Javadoc

JDK <= 1.5

System.arraycopy(Object[] src, int srcStartIndex, Object[] dest, int dstStartIndex, int lengthOfCopiedIndices);

Javadoc

edited Jan 07 '17 at 10:43

Flow

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answered Dec 14 '10 at 13:22

jmj

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I was having some issues with not having Object[]s in my Arrays.copyOfRange. Check your imports to ensure you are using java.util.Arrays. Somehow a different Arrays version got imported and I wasted 15 minutes checking JREs and JDKs for the issue. – NuclearPeon Oct 09 '13 at 21:30
@NuclearPeon Thank you!!! Would have taken me a long while before I figured it out myself. Eclipse automatically imported `org.bouncycastle.util.Arrays`. – Snackoverflow Jul 19 '17 at 12:30
This is actually a copy of a part of an array. A sub-array would be pointing to the original array like a sub-list. Changing an array element will not affect the original array whereas in a sub-array it would. Also it has performance implications as not only the pointers are copied, but all elements (for objects shallow copy). – Gunnar Bernstein Feb 17 '23 at 06:38

score 146 · Answer 2 · answered Dec 14 '10 at 13:48

146

Arrays.copyOfRange(..) was added in Java 1.6. So perhaps you don't have the latest version. If it's not possible to upgrade, look at System.arraycopy(..)

answered Dec 14 '10 at 13:48

Bozho

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@Sami either upgrade to 1.6 or see this doc for reference http://download.oracle.com/javase/1.4.2/docs/api/java/lang/System.html – jmj Dec 14 '10 at 13:54
4

Which vendor is your JDK from. Sun/Oracle never released a version 4.00.28 and google couldn't find it either. – Peter Lawrey Dec 14 '10 at 14:16
copyOfRange nulls trailing elements if they are out of source array range instead of allocating a smaller array :( – Daniil Iaitskov Jun 26 '15 at 14:59
22

someone should add in the answer that while "start-index" is inclusive, "end-index" is *exclusive* – Yan King Yin Oct 09 '15 at 12:14
@YanKingYin you are correct--this is precisely what I was reading the comments for :) – Ben Kushigian Aug 30 '18 at 11:06

score 22 · Answer 3 · edited Sep 20 '14 at 09:30

22

Yes, it's called System.arraycopy(Object, int, Object, int, int) .

It's still going to perform a loop somewhere though, unless this can get optimized into something like REP STOSW by the JIT (in which case the loop is inside the CPU).

int[] src = new int[] {1, 2, 3, 4, 5};
int[] dst = new int[3];

System.arraycopy(src, 1, dst, 0, 3); // Copies 2, 3, 4 into dst

edited Sep 20 '14 at 09:30

KNU

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answered Dec 14 '10 at 13:22

Gerco Dries

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enator · Answer 4 · 2020-02-09T07:09:13.580

JDK >= 1.8

I agree with all the answers above. There is also a nice way with Java 8 Streams:

int[] subArr = IntStream.range(startInclusive, endExclusive)
                        .map(i -> src[i])
                        .toArray();

The benefit about this is, it can be useful for many different types of "src" array and helps to improve writing pipeline operations on the stream.

Not particular about this question, but for example, if the source array was double[] and we wanted to take average() of the sub-array:

double avg = IntStream.range(startInclusive, endExclusive)
                    .mapToDouble(index -> src[index])
                    .average()
                    .getAsDouble();

Good idea to use streams. One could also use `Stream.of(source).skip(start).limit(count).toArray(Foo[]::new)`. — Martin, Jan 04 '22 at 21:41

score 8 · Answer 5 · answered Jun 01 '15 at 17:14

8

Using Apache ArrayUtils downloadable at this link you can easy use the method

subarray(boolean[] array, int startIndexInclusive, int endIndexExclusive)

"boolean" is only an example, there are methods for all primitives java types

answered Jun 01 '15 at 17:14

Alessandro Muzzi

808
1
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score 4 · Answer 6 · edited Dec 14 '10 at 14:00

4

int newArrayLength = 30; 

int[] newArray = new int[newArrayLength];

System.arrayCopy(oldArray, 0, newArray, 0, newArray.length);

edited Dec 14 '10 at 14:00

Riduidel

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answered Dec 14 '10 at 13:51

Milan Jaros

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score 2 · Answer 7 · answered Dec 14 '10 at 13:52

2

The code is correct so I'm guessing that you are using an older JDK. The javadoc for that method says it has been there since 1.6. At the command line type:

java -version

I'm guessing that you are not running 1.6

answered Dec 14 '10 at 13:52

Merky

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score 1 · Answer 8 · answered Dec 14 '10 at 13:50

1

I you are using java prior to version 1.6 use System.arraycopy() instead. Or upgrade your environment.

answered Dec 14 '10 at 13:50

AlexR

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score 0 · Answer 9 · answered Feb 28 '23 at 15:45

0

For Java >= 1.8

Arrays.stream(array, incIndex, exclusiveIndex)

answered Feb 28 '23 at 15:45

Nikita Zamalyutdinov

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score 0 · Answer 10 · answered Jul 06 '23 at 17:18

0

OP said they didn't want a for loop but in case anyone does:

int[] subArr = new int[end - start];

for (int i = 0; i < end - start; i++){
    subArr[i] = sourceArr[i + start];
}

answered Jul 06 '23 at 17:18

Hsabes

21
3

How to create a sub array from another array in Java?

10 Answers10

JDK > 1.5

JDK <= 1.5

Linked

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