How do I initialize a byte array in Java?

I have to store some constant values (UUIDs) in byte array form in java, and I'm wondering what the best way to initialize those static arrays would be. This is how I'm currently doing it, but I feel like there must be a better way.

private static final byte[] CDRIVES = new byte[] < (byte)0xe0, 0x4f, (byte)0xd0, 0x20, (byte)0xea, 0x3a, 0x69, 0x10, (byte)0xa2, (byte)0xd8, 0x08, 0x00, 0x2b, 0x30, 0x30, (byte)0x9d >; private static final byte[] CMYDOCS = new byte[] < (byte)0xba, (byte)0x8a, 0x0d, 0x45, 0x25, (byte)0xad, (byte)0xd0, 0x11, (byte)0x98, (byte)0xa8, 0x08, 0x00, 0x36, 0x1b, 0x11, 0x03 >; private static final byte[] IEFRAME = new byte[] < (byte)0x80, 0x53, 0x1c, (byte)0x87, (byte)0xa0, 0x42, 0x69, 0x10, (byte)0xa2, (byte)0xea, 0x08, 0x00, 0x2b, 0x30, 0x30, (byte)0x9d >; . and so on 

private static final byte[] CDRIVES = new byte[] < "0xe04fd020ea3a6910a2d808002b30309d" >; 

Since they're declared as static final , this might already be the most proper way; the accepted answer completely ignores these keywords and would not even work with them.

11 Answers 11

You can use an utility function to convert from the familiar hexa string to a byte[] . When used to define a final static constant, the performance cost is irrelevant.

Since Java 17

There's now java.util.HexFormat which lets you do

byte[] CDRIVES = HexFormat.of().parseHex("e04fd020ea3a6910a2d808002b30309d"); 

This utility class lets you specify a format which is handy if you find other formats easier to read or when you're copy-pasting from a reference source:

byte[] CDRIVES = HexFormat.ofDelimiter(":") .parseHex("e0:4f:d0:20:ea:3a:69:10:a2:d8:08:00:2b:30:30:9d"); 

Before Java 17

byte[] CDRIVES = hexStringToByteArray("e04fd020ea3a6910a2d808002b30309d"); 

I insert it here for maximum readability :

public static byte[] hexStringToByteArray(String s) < int len = s.length(); byte[] data = new byte[len / 2]; for (int i = 0; i < len; i += 2) < data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) return data; > 

byte[] myvar = "Any String you want".getBytes(); 

String literals can be escaped to provide any character:

byte[] CDRIVES = "\u00e0\u004f\u00d0\u0020\u00ea\u003a\u0069\u0010\u00a2\u00d8\u0008\u0000\u002b\u0030\u0030\u009d".getBytes(); 

Look at the question's title. Then look back at this answer. Now tell me, what's wrong about it? It might not solve the poster's particular issue, but it sure solved mine. I needed to transform a string into a byte array to use as a seed for a pseudorandom number generator and this worked like a charm.

@e18r It is generating bytes, yes, but you don't know which since this depence on the default charset. At least use .getBytes(desiredEncoding).

@petmez dumb question: in JAVA, is something like "".getBytes(UTF_8)); (getBytes on an empty string) a safe thing to do? is it 'legal'? Or can I just do: = new byte[0]; ?

In Java 6, there is a method doing exactly what you want:

private static final byte[] CDRIVES = javax.xml.bind.DatatypeConverter.parseHexBinary("e04fd020ea3a6910a2d808002b30309d") 

Alternatively you could use Google Guava:

import com.google.common.io.BaseEncoding; private static final byte[] CDRIVES = BaseEncoding.base16().lowerCase().decode("E04FD020ea3a6910a2d808002b30309d".toLowerCase()); 

The Guava method is overkill, when you are using small arrays. But Guava has also versions that can parse input streams. This is a nice feature when dealing with big hexadecimal inputs.

The Guava example doesn't quite work as written - it needs to be base16().lowerCase().decode(. ) if you have lower case hex digits. docs.guava-libraries.googlecode.com/git/javadoc/com/google/…

@PeterDeGlopper Good finding, I've updated the answer so the code now handles strings with both lower and upper case characters.

You can use the Java UUID class to store these values, instead of byte arrays:

UUID public UUID(long mostSigBits, long leastSigBits) 

Constructs a new UUID using the specified data. mostSigBits is used for the most significant 64 bits of the UUID and leastSigBits becomes the least significant 64 bits of the UUID.

Smallest internal type, which at compile time can be assigned by unsigned hex numbers is char, as

private static final char[] CDRIVES_char = new char[] ; 

In order to have an equivalent byte array one might deploy conversions as

public static byte[] charToByteArray(char[] x) < final byte[] res = new byte[x.length]; for (int i = 0; i < x.length; i++) < res[i] = (byte) x[i]; >return res; > public static byte[][] charToByteArray(char[][] x) < final byte[][] res = new byte[x.length][]; for (int i = 0; i < x.length; i++) < res[i] = charToByteArray(x[i]); >return res; > 

A solution with no libraries, dynamic length returned, unsigned integer interpretation (not two's complement)

 public static byte[] numToBytes(int num)< if(num == 0)< return new byte[]<>; >else if(num < 256)< return new byte[]< (byte)(num) >; >else if(num < 65536)< return new byte[]< (byte)(num >>> 8),(byte)num >; >else if(num < 16777216)< return new byte[]< (byte)(num >>> 16),(byte)(num >>> 8),(byte)num >; >else< // up to 2,147,483,647 return new byte[]< (byte)(num >>> 24),(byte)(num >>> 16),(byte)(num >>> 8),(byte)num >; > > 

You can use this utility function:

public static byte[] fromHexString(String src)

Unlike variants of Denys Séguret and stefan.schwetschke, it allows inserting separator symbols (spaces, tabs, etc.) into the input string, making it more readable.

Example of usage:

private static final byte[] CDRIVES = fromHexString("e0 4f d0 20 ea 3a 69 10 a2 d8 08 00 2b 30 30 9d"); private static final byte[] CMYDOCS = fromHexString("BA8A0D4525ADD01198A80800361B1103"); private static final byte[] IEFRAME = fromHexString("80531c87 a0426910 a2ea0800 2b30309d");