How to convert a byte array to its numeric value Java

Question

I have an 8 byte array and I want to convert it to its corresponding numeric value   e g   byte   by   new byte 8       the byte array is stored in  by      CONVERSION OPERATION    return the numeric value   I want a method that will perform the above conversion operation

User · Accepted Answer

Assuming the first byte is the least significant byte:

long value = 0;
for (int i = 0; i < by.length; i++)
{
   value += ((long) by[i] & 0xffL) << (8 * i);
}

Is the first byte the most significant, then it is a little bit different:

long value = 0;
for (int i = 0; i < by.length; i++)
{
   value = (value << 8) + (by[i] & 0xff);
}

Replace long with BigInteger, if you have more than 8 bytes.

Thanks to Aaron Digulla for the correction of my errors.

User · Answer

If this is an 8-bytes numeric value  you can try   BigInteger n   new BigInteger byteArray     If this is an UTF-8 character buffer  then you can try   BigInteger n   new BigInteger new String byteArray   UTF-8

User · Answer

public static long byteArrayToLong byte   bytes        return   long   bytes 0    lt  lt  56                   long  bytes 1   amp  0xFF   lt  lt  48                  long   bytes 2   amp  0xFF   lt  lt  40                  long   bytes 3   amp  0xFF   lt  lt  32                  long   bytes 4   amp  0xFF   lt  lt  24                  bytes 5   amp  0xFF   lt  lt  16                  bytes 6   amp  0xFF   lt  lt  8                 bytes 7   amp  0xFF      convert bytes array  long is 8 bytes  to long

User · Answer

Complete java converter code for all primitive types to from arrays http   www daniweb com code snippet216874 html

User · Answer

One could use the Buffers that are provided as part of the java nio package to perform the conversion   Here  the source byte   array has a of length 8  which is the size that corresponds with a long value   First  the byte   array is wrapped in a ByteBuffer  and then the ByteBuffer getLong method is called to obtain the long value   ByteBuffer bb   ByteBuffer wrap new byte    0  0  0  0  0  0  0  4    long l   bb getLong     System out println l     Result  4   I d like to thank dfa for pointing out the ByteBuffer getLong method in the comments     Although it may not be applicable in this situation  the beauty of the Buffers come with looking at an array with multiple values   For example  if we had a 8 byte array  and we wanted to view it as two int values  we could wrap the byte   array in an ByteBuffer  which is viewed as a IntBuffer and obtain the values by IntBuffer get   ByteBuffer bb   ByteBuffer wrap new byte    0  0  0  1  0  0  0  4    IntBuffer ib   bb asIntBuffer    int i0   ib get 0   int i1   ib get 1    System out println i0   System out println i1     Result   1 4

User · Answer

You can also use BigInteger for variable length bytes  You can convert it to Long  Integer or Short  whichever suits your needs   new BigInteger bytes  intValue      or to denote polarity   new BigInteger 1  bytes  intValue

User · Answer

Each cell in the array is treated as unsigned int   private int unsignedIntFromByteArray byte   bytes    int res   0  if  bytes    null      return res    for  int i 0 i lt bytes length i         res   res     bytes i   amp  0xff   lt  lt  i 8     return res

User · Answer

Simply  you could use or refer to guava lib provided by google  which offers utiliy methods for conversion between long and byte array  My client code       long content   212000607777l      byte   numberByte   Longs toByteArray content       logger info Longs fromByteArray numberByte

[java] How to convert a byte array to its numeric value (Java)?

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