[java] 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" };

This question is related to java arrays byte

The answer is


Using a function converting an hexa string to byte[], you could do

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

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?

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;
}

If you let CDRIVES static and final, the performance drop is irrelevant.


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();

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.


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 hex numbers is char, as

private static final char[] CDRIVES_char = new char[] {0xe0, 0xf4, ...};

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) {
    byte[] biBytes = new BigInteger("10" + src.replaceAll("\\s", ""), 16).toByteArray();
    return Arrays.copyOfRange(biBytes, 1, biBytes.length);
}

Unlike variants of Denys S├ęguret 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");

As far as a clean process is concerned you can use ByteArrayOutputStream object...

ByteArrayOutputStream bObj = new ByteArrayOutputStream();
bObj.reset();

//write all the values to bObj one by one using

bObj.write(byte value)

// when done you can get the byte[] using

CDRIVES = bObj.toByteArray();

//than you can repeat the similar process for CMYDOCS and IEFRAME as well,

NOTE This is not an efficient solution if you really have small array.


My preferred option in this circumstance is to use org.apache.commons.codec.binary.Hex which has useful APIs for converting between Stringy hex and binary. For example:

  1. Hex.decodeHex(char[] data) which throws a DecoderException if there are non-hex characters in the array, or if there are an odd number of characters.

  2. Hex.encodeHex(byte[] data) is the counterpart to the decode method above, and spits out the char[].

  3. Hex.encodeHexString(byte[] data) which converts back from a byte array to a String.

Usage: Hex.decodeHex("dd645a2564cbe648c8336d2be5eafaa6".toCharArray())


private static final int[] CDRIVES = new int[] {0xe0, 0xf4, ...};

and after access convert to byte.


Questions with java tag:

Under what circumstances can I call findViewById with an Options Menu / Action Bar item? How much should a function trust another function How to implement a simple scenario the OO way Two constructors How do I get some variable from another class in Java? this in equals method How to split a string in two and store it in a field How to do perspective fixing? String index out of range: 4 My eclipse won't open, i download the bundle pack it keeps saying error log getting " (1) no such column: _id10 " error Instantiating a generic type When to create variables (memory management) java doesn't run if structure inside of onclick listener String method cannot be found in a main class method Are all Spring Framework Java Configuration injection examples buggy? Calling another method java GUI I need to know how to get my program to output the word i typed in and also the new rearranged word using a 2D array Java and unlimited decimal places? Read input from a JOptionPane.showInputDialog box Cannot retrieve string(s) from preferences (settings) strange error in my Animation Drawable Two Page Login with Spring Security 3.2.x Hadoop MapReduce: Strange Result when Storing Previous Value in Memory in a Reduce Class (Java) Got a NumberFormatException while trying to parse a text file for objects Best way for storing Java application name and version properties Call japplet from jframe FragmentActivity to Fragment Comparing two joda DateTime instances Maven dependencies are failing with a 501 error IntelliJ: Error:java: error: release version 5 not supported Has been compiled by a more recent version of the Java Runtime (class file version 57.0) Why am I getting Unknown error in line 1 of pom.xml? Gradle: Could not determine java version from '11.0.2' Error: Java: invalid target release: 11 - IntelliJ IDEA Android Gradle 5.0 Update:Cause: org.jetbrains.plugins.gradle.tooling.util Why is 2 * (i * i) faster than 2 * i * i in Java? must declare a named package eclipse because this compilation unit is associated to the named module How do I install Java on Mac OSX allowing version switching? How to install JDK 11 under Ubuntu? Java 11 package javax.xml.bind does not exist IntelliJ can't recognize JavaFX 11 with OpenJDK 11 Difference between OpenJDK and Adoptium/AdoptOpenJDK OpenJDK8 for windows How to allow all Network connection types HTTP and HTTPS in Android (9) Pie? Find the smallest positive integer that does not occur in a given sequence Error: JavaFX runtime components are missing, and are required to run this application with JDK 11 How to uninstall Eclipse? Failed to resolve: com.google.firebase:firebase-core:16.0.1 How to resolve Unable to load authentication plugin 'caching_sha2_password' issue

Questions with arrays tag:

PHP array value passes to next row Use NSInteger as array index How do I show a message in the foreach loop? Objects are not valid as a React child. If you meant to render a collection of children, use an array instead Iterating over arrays in Python 3 Best way to "push" into C# array Sort Array of object by object field in Angular 6 Checking for duplicate strings in JavaScript array what does numpy ndarray shape do? How to round a numpy array? How to update an "array of objects" with Firestore? How to increment a letter N times per iteration and store in an array? Cloning an array in Javascript/Typescript use Lodash to sort array of object by value TypeScript enum to object array How do I check whether an array contains a string in TypeScript? How to use forEach in vueJs? Program to find largest and second largest number in array How to plot an array in python? How to add and remove item from array in components in Vue 2 console.log(result) returns [object Object]. How do I get result.name? How to map an array of objects in React How to define Typescript Map of key value pair. where key is a number and value is an array of objects Removing object from array in Swift 3 How to group an array of objects by key Find object by its property in array of objects with AngularJS way Getting an object array from an Angular service push object into array How to get first and last element in an array in java? Add key value pair to all objects in array How to convert array into comma separated string in javascript Showing ValueError: shapes (1,3) and (1,3) not aligned: 3 (dim 1) != 1 (dim 0) Angular 2 declaring an array of objects How can I loop through enum values for display in radio buttons? How to convert JSON object to an Typescript array? Angular get object from array by Id Add property to an array of objects Declare an array in TypeScript ValueError: all the input arrays must have same number of dimensions How to convert an Object {} to an Array [] of key-value pairs in JavaScript Check if a value is in an array or not with Excel VBA TypeScript add Object to array with push Filter array to have unique values remove first element from array and return the array minus the first element merge two object arrays with Angular 2 and TypeScript? Creating an Array from a Range in VBA "error: assignment to expression with array type error" when I assign a struct field (C) How do I filter an array with TypeScript in Angular 2? How to generate range of numbers from 0 to n in ES2015 only? TypeError: Invalid dimensions for image data when plotting array with imshow()

Questions with byte tag:

Convert bytes to int? TypeError: a bytes-like object is required, not 'str' when writing to a file in Python3 How many bits is a "word"? How many characters can you store with 1 byte? Save byte array to file Convert dictionary to bytes and back again python? How do I get total physical memory size using PowerShell without WMI? Hashing with SHA1 Algorithm in C# How to create a byte array in C++? Converting string to byte array in C# Correct way to convert size in bytes to KB, MB, GB in JavaScript How to Get True Size of MySQL Database? Does .NET provide an easy way convert bytes to KB, MB, GB, etc.? How to convert between bytes and strings in Python 3? C program to check little vs. big endian How to store a byte array in Javascript How to convert a byte to its binary string representation Is the size of C "int" 2 bytes or 4 bytes? What does value & 0xff do in Java? How do I initialize a byte array in Java? How to convert from []byte to int in Go Programming Char array to hex string C++ How to convert byte[] to InputStream? Byte array to image conversion Convert bytes to bits in python How to know the size of the string in bytes? How to convert hex strings to byte values in Java Convert a String to a byte array and then back to the original String How to Convert Int to Unsigned Byte and Back Byte Array in Python Java Byte Array to String to Byte Array Write bytes to file Java - Convert int to Byte Array of 4 Bytes? What is the difference between a string and a byte string? C++ int to byte array Appending a byte[] to the end of another byte[] How do you specify a byte literal in Java? Convert any object to a byte[] How many bits or bytes are there in a character? How do I convert Long to byte[] and back in java Java: object to byte[] and byte[] to object converter (for Tokyo Cabinet) How to declare and use 1D and 2D byte arrays in Verilog? How to read a file byte by byte in Python and how to print a bytelist as a binary? Saving any file to in the database, just convert it to a byte array? How many bytes in a JavaScript string? Java integer to byte array Convert integer into byte array (Java) #1071 - Specified key was too long; max key length is 767 bytes How to print bytes in hexadecimal using System.out.println? How to Convert unsigned char* to std::string in C++?