Convert a byte array to integer in Java and vice versa

Question

I want to store some data into byte arrays in Java  Basically just numbers which can take up to 2 Bytes per number   I d like to know how I can convert an integer into a 2 byte long byte array and vice versa  I found a lot of solutions googling but most of them don t explain what happens in the code  There s a lot of shifting stuff I don t really understand so I would appreciate a basic explanation

User · Answer

You can also use BigInteger for variable length bytes. You can convert it to long, int or short, whichever suits your needs.

new BigInteger(bytes).intValue();

or to denote polarity:

new BigInteger(1, bytes).intValue();

To get bytes back just:

new BigInteger(bytes).toByteArray()

User · Answer

byte   toByteArray int value         return  ByteBuffer allocate 4  putInt value  array       byte   toByteArray int value        return new byte               byte  value  gt  gt  24            byte  value  gt  gt  16            byte  value  gt  gt  8            byte value       int fromByteArray byte   bytes         return ByteBuffer wrap bytes  getInt         packing an array of 4 bytes to an int  big endian  minimal parentheses    operator precedence   lt  lt    amp         when operators of equal precedence  here bitwise OR  appear in the same expression  they are evaluated from left to right int fromByteArray byte   bytes         return bytes 0   lt  lt  24    bytes 1   amp  0xFF   lt  lt  16    bytes 2   amp  0xFF   lt  lt  8    bytes 3   amp  0xFF         packing an array of 4 bytes to an int  big endian  clean code int fromByteArray byte   bytes         return   bytes 0   amp  0xFF   lt  lt  24                   bytes 1   amp  0xFF   lt  lt  16                   bytes 2   amp  0xFF   lt  lt  8                    bytes 3   amp  0xFF   lt  lt  0        When packing signed bytes into an int  each byte needs to be masked off because it is sign-extended to 32 bits  rather than zero-extended  due to the arithmetic promotion rule  described in JLS  Conversions and Promotions    There s an interesting puzzle related to this described in Java Puzzlers   A Big Delight in Every Byte   by Joshua Bloch and Neal Gafter   When comparing a byte value to an int value  the byte is sign-extended to an int and then this value is compared to the other int  byte   bytes         if  bytes 0     0xFF          dead code  bytes 0  is in the range  -128 127  and thus never equal to 255     Note that all numeric types are signed in Java with exception to char being a 16-bit unsigned integer type

User · Answer

Use the classes found in the java nio namespace  in particular  the ByteBuffer   It can do all the work for you   byte   arr     0x00  0x01    ByteBuffer wrapped   ByteBuffer wrap arr      big-endian by default short num   wrapped getShort       1  ByteBuffer dbuf   ByteBuffer allocate 2   dbuf putShort num   byte   bytes   dbuf array         0  1

User · Answer

Someone with a requirement where they have to read from bits  lets say you have to read from only 3 bits but you need signed integer then use following   data is of type  java util BitSet  new BigInteger data toByteArray  intValue    lt  lt  32 - 3  gt  gt  32 - 3   The magic number 3 can be replaced with the number of bits  not bytes  you are using

User · Answer

length should be less than 4  for int      public long byteToInt byte   bytes  int length            int val   0          if length gt 4  throw new RuntimeException  Too big to fit in int            for  int i   0  i  lt  length  i                  val val lt  lt 8              val val  bytes i   amp  0xFF                     return val

User · Answer

i think this is a best mode to cast to int     public int ByteToint Byte B           String comb          int out 0          comb B             salida  Integer parseInt comb           out out 128          return out          first comvert byte to String   comb B       next step is comvert to a int  out  Integer parseInt comb     but byte is in rage of -128 to 127 for this reasone  i think is better use rage 0 to 255 and you only need to do this   out out 256

User · Answer

A basic implementation would be something like this   public class Test       public static void main String   args            int   input   new int     0x1234  0x5678  0x9abc            byte   output   new byte input length   2            for  int i   0  j   0  i  lt  input length  i    j  2                output j     byte  input i   amp  0xff               output j 1     byte   input i   gt  gt  8   amp  0xff                      for  int i   0  i  lt  output length  i                System out format   02x n  output i              In order to understand things you can read this WP article  http   en wikipedia org wiki Endianness  The above source code will output 34 12 78 56 bc 9a  The first 2 bytes  34 12  represent the first integer  etc  The above source code encodes integers in little endian format

User · Answer

As often  guava has what you need    To go from byte array to int  Ints fromBytesArray  doc here   To go from int to byte array  Ints toByteArray  doc here

[java] Convert a byte array to integer in Java and vice versa

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