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);
    }
}

Flow · Accepted Answer · 2017-01-07 10:43:45Z

419

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 7, 2017 at 10:43

Flow

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answered Dec 14, 2010 at 13:22

Jigar Joshi

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4 Comments

NuclearPeon Over a year ago

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.

Snackoverflow Over a year ago

@NuclearPeon Thank you!!! Would have taken me a long while before I figured it out myself. Eclipse automatically imported org.bouncycastle.util.Arrays.

Gunnar Bernstein Over a year ago

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).

talentless Over a year ago

I needed to copy an array into an already existing larger array . In my use case, System.arraycopy() was exactly what I needed.

Bozho · Accepted Answer · 2010-12-14 13:48:05Z

147

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, 2010 at 13:48

Bozho

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5 Comments

Jigar Joshi Over a year ago

@Sami either upgrade to 1.6 or see this doc for reference download.oracle.com/javase/1.4.2/docs/api/java/lang/System.html

Peter Lawrey Over a year ago

Which vendor is your JDK from. Sun/Oracle never released a version 4.00.28 and google couldn't find it either.

Daniil Iaitskov Over a year ago

copyOfRange nulls trailing elements if they are out of source array range instead of allocating a smaller array :(

Yan King Yin Over a year ago

someone should add in the answer that while "start-index" is inclusive, "end-index" is exclusive

Ben Kushigian Over a year ago

@YanKingYin you are correct--this is precisely what I was reading the comments for :)

KNU · Accepted Answer · 2014-09-20 09:30:31Z

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, 2014 at 9:30

KNU

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answered Dec 14, 2010 at 13:22

Gerco Dries

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Comments

enator · Accepted Answer · 2020-02-09 07:09:13Z

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).

Alessandro Muzzi · Accepted Answer · 2015-06-01 17:14:04Z

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 1, 2015 at 17:14

Alessandro Muzzi

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Comments

Riduidel · Accepted Answer · 2010-12-14 14:00:33Z

4

int newArrayLength = 30; 

int[] newArray = new int[newArrayLength];

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

edited Dec 14, 2010 at 14:00

Riduidel

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answered Dec 14, 2010 at 13:51

Milan Jaros

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Comments

Merky · Accepted Answer · 2010-12-14 13:52:26Z

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, 2010 at 13:52

Merky

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Comments

Nikita Zamalyutdinov · Accepted Answer · 2023-02-28 15:45:36Z

2

For Java >= 1.8

Arrays.stream(array, incIndex, exclusiveIndex)

answered Feb 28, 2023 at 15:45

Nikita Zamalyutdinov

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Comments

AlexR · Accepted Answer · 2010-12-14 13:50:50Z

1

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

answered Dec 14, 2010 at 13:50

AlexR

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Comments

Hsabes · Accepted Answer · 2023-07-06 17:18:51Z

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 6, 2023 at 17:18

Hsabes

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