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

Is there anything I could use that may be less efficient, but would look cleaner? for example:

private static final byte[] CDRIVES =
    new byte[] { "0xe04fd020ea3a6910a2d808002b30309d" };

Solution 1:

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

I'd suggest you use the function defined by Dave L in Convert a string representation of a hex dump to a byte array using Java?

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) << 4)
                             + Character.digit(s.charAt(i+1), 16));
    }
    return data;
}

Solution 2:

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();

Solution 3:

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.