How do I initialize a byte array in Java

Question

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

User · Answer

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  guret 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

User · Answer

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

User · Answer

private static final int   CDRIVES   new int    0xe0  0xf4          and after access convert to byte

User · Answer

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  lt  256           return new byte     byte  num          else if num  lt  65536           return new byte     byte  num  gt  gt  gt  8   byte num         else if num  lt  16777216           return new byte     byte  num  gt  gt  gt  16   byte  num  gt  gt  gt  8   byte num         else     up to 2 147 483 647         return new byte     byte  num  gt  gt  gt  24   byte  num  gt  gt  gt  16   byte  num  gt  gt  gt  8   byte num

User · Answer

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

User · Answer

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  lt  len  i    2            data i   2     byte    Character digit s charAt i   16   lt  lt  4                                 Character digit s charAt i 1   16              return data      If you let CDRIVES static and final  the performance drop is irrelevant

User · Answer

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    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  Hex encodeHex byte   data  is the counterpart to the decode method above  and spits out the char    Hex encodeHexString byte   data  which converts back from a byte array to a String    Usage  Hex decodeHex  dd645a2564cbe648c8336d2be5eafaa6  toCharArray

User · Answer

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

User · Answer

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

User · Answer

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  lt  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  lt  x length  i                  res i    charToByteArray x i              return res

[java] How do I initialize a byte array in Java?

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