How to convert byte[] to Byte[] and the other way around?

Question

How to convert byte[] to Byte[] and also Byte[] to byte[], in the case of not using any 3rd party library?

Is there a way to do it fast just using the standard library?

Solution 1

Byte class is a wrapper for the primitive byte. This should do the work:

byte[] bytes = new byte[10];
Byte[] byteObjects = new Byte[bytes.length];

int i=0;    
// Associating Byte array values with bytes. (byte[] to Byte[])
for(byte b: bytes)
   byteObjects[i++] = b;  // Autoboxing.

....

int j=0;
// Unboxing Byte values. (Byte[] to byte[])
for(Byte b: byteObjects)
    bytes[j++] = b.byteValue();

Solution 2

byte[] to Byte[] :

byte[] bytes = ...;
Byte[] byteObject = ArrayUtils.toObject(bytes);

Byte[] to byte[] :

Byte[] byteObject = new Byte[0];
byte[] bytes = ArrayUtils.toPrimitive(byteObject);

Solution 3

Java 8 solution:

Byte[] toObjects(byte[] bytesPrim) {
    Byte[] bytes = new Byte[bytesPrim.length];
    Arrays.setAll(bytes, n -> bytesPrim[n]);
    return bytes;
}

Unfortunately, you can't do this to convert from Byte[] to byte[]. Arrays has setAll for double[], int[], and long[], but not for other primitive types.

Solution 4

You could use the toPrimitive method in the Apache Commons lang library ArrayUtils class, As suggested here - Java - Byte[] to byte[]

Solution 5

byte[] toPrimitives(Byte[] oBytes)
{

    byte[] bytes = new byte[oBytes.length];
    for(int i = 0; i < oBytes.length; i++){
        bytes[i] = oBytes[i];
    }
    return bytes;

}

Inverse:

//byte[] to Byte[]
Byte[] toObjects(byte[] bytesPrim) {

    Byte[] bytes = new Byte[bytesPrim.length];
    int i = 0;
    for (byte b : bytesPrim) bytes[i++] = b; //Autoboxing
    return bytes;

}

View more solutions

Comments

[Dunes]

Would definitely recommend Byte.valueOf(b) over new Byte(b). I would be surprised if the Byte class didn't cache every single value for a byte.

[Edwin Dalorzo]

I believe that it might be better to use Byte.valueOf(byte). JavaDocs say that this method should generally be used in preference to the constructor Byte(byte), as this method is likely to yield significantly better space and time performance since all byte values are cached.

[Code-Apprentice]

With autoboxing, you can simply do byteObjects[i++] = b;

[BalusC]

I'd use new Byte[bytes.length]; instead of new Byte[10]; to keep it sensible.

[user504342]

This answer isn't correct. The i++ and j++ in the for-each loop don't do anything useful. You need to use the basic for-loop: for (int i=0; i<bytes.length;i++) { byteObjects[i] = b[i]; }. Same goes for unboxing.

[Juvanis]

@user504342 have you ever debugged my code? with my code i and j goes from 0 to 10 and handles the job.

[user504342]

@Juvanis aha, I see that you use two "counters" in the for-loop: one to iterate over the primitive byte array and/or Byte object array, and another one for incrementing the index of the primitive byte array and/or Byte object array. To me, this is bad practice. If this code is maintained by others, and someone would modify the counter "i" from 0 to another value, or would change the i++ into ++i, the indexes no longer match. I am not advocating anyone should modify the code in the first place, but it's a common pitfall for beginners. My suggestion keeps the indexes of both arrays in sync.

[ARRG]

This is actually the best answer, at least for anyone for whom adding a dependency to commons-lang isn't an issue.

[mvorisek]

Why this is not the best answer? Any performace reason or just answered later?

[mvorisek]

Because the ArrayUtils are not a part of Java, but Apache lib.

[ElectRocnic]

and the other way round?

[mkalmo]

I think you can't get byte[] from Stream. Stream api has mapToInt(), mapToDouble() and mapToLong() methods but not mapToByte().

[Alex8752]

I agree with @mvorisek, this should be considered the best answer. Just add org.apache.commons.lang3.ArrayUtils

[Liscare]

Best answer for me. Simple code and no third-party library.

[Binita Bharati]

Unfortunately, ArrayUtils is not part of standard Java packages.

[Steve Bosman]

how does this have upvotes when it is code that doesn't work?

[Frédéric Nobre]

apache commons lang is a great package that should be part of any java project.