Can we make unsigned byte in Java

Question

I am trying to convert a signed byte in unsigned  The problem is the data I am receiving is unsigned and Java does not support unsigned byte  so when it reads the data it treats it as signed   I tried it to convert it by the following solution I got from Stack nbsp Overflow   public static int unsignedToBytes byte a        int b   a  amp  0xFF      return b      But when again it s converted in byte  I get the same signed data  I am trying to use this data as a parameter to a function of Java that accepts only a byte as parameter  so I can t use any other data type  How can I fix this problem

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There are no primitive unsigned bytes in Java  The usual thing is to cast it to bigger type   int anUnsignedByte    int  aSignedByte  amp  0xff

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I think the other answers have covered memory representation and how you handle these depends on the context of how you plan on using it  I ll add that Java 8 added some support for dealing with unsigned types  In this case  you could use Byte toUnsignedInt  int unsignedInt   Byte toUnsignedInt myByte

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Adamski provided the best answer  but it is not quite complete  so read his reply  as it explains the details I m not   If you have a system function that requires an unsigned byte to be passed to it  you can pass a signed byte as it will automatically treat it as an unsigned byte   So if a system function requires four bytes  for example  192 168 0 1 as unsigned bytes you can pass -64 -88 0 1  and the function will still work  because the act of passing them to the function will un-sign them   However you are unlikely to have this problem as system functions are hidden behind classes for cross-platform compatibility  though some of the java io read methods return unsighed bytes as an int   If you want to see this working  try writing signed bytes to a file and read them back as unsigned bytes

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As per limitations in Java  unsigned byte is almost impossible in the current data-type format  You can go for some other libraries of another language for what you are implementing and then you can call them using JNI

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If you have a function which must be passed a signed byte  what do you expect it to do if you pass an unsigned byte     Why can t you use any other data type   Unsually you can use a byte as an unsigned byte with simple or no translations   It all depends on how it is used  You would need to clarify what you indend to do with it

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I am trying to use this data as a parameter to a function of Java that accepts only a byte as parameter   This is not substantially different from a function accepting an integer to which you want to pass a value larger than 2 32-1   That sounds like it depends on how the function is defined and documented  I can see three possibilities    It may explicitly document that the function treats the byte as an unsigned value  in which case the function probably should do what you expect but would seem to be implemented wrong  For the integer case  the function would probably declare the parameter as an unsigned integer  but that is not possible for the byte case  It may document that the value for this argument must be greater than  or perhaps equal to  zero  in which case you are misusing the function  passing an out-of-range parameter   expecting it to do more than it was designed to do  With some level of debugging support you might expect the function to throw an exception or fail an assertion  The documentation may say nothing  in which case a negative parameter is  well  a negative parameter and whether that has any meaning depends on what the function does  If this is meaningless then perhaps the function should really be defined documented as  2   If this is meaningful in an nonobvious manner  e g  non-negative values are used to index into an array  and negative values are used to index back from the end of the array so -1 means the last element  the documentation should say what it means and I would expect that it isn t what you want it to do anyway

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The fact that primitives are signed in Java is irrelevant to how they re represented in memory   transit - a byte is merely 8 bits and whether you interpret that as a signed range or not is up to you  There is no magic flag to say  this is signed  or  this is unsigned    As primitives are signed the Java compiler will prevent you from assigning a value higher than  127 to a byte  or lower than -128   However  there s nothing to stop you downcasting an int  or short  in order to achieve this   int i   200     0000 0000 0000 0000 0000 0000 1100 1000  200  byte b    byte  200     1100 1000  -56 by Java specification  200 by convention         Will print a negative int -56 because upcasting byte to int does    so called  sign extension  which yields those bits     1111 1111 1111 1111 1111 1111 1100 1000  -56        But you could still choose to interpret this as  200      System out println b       -56         Will print a positive int 200 because bitwise AND with 0xFF will    zero all the 24 most significant bits that     a  were added during upcasting to int which took place silently       just before evaluating the bitwise AND operator        So the  b  amp  0xFF  is equivalent with    int  b   amp  0xFF      b  were set to 1s because of  sign extension  during the upcasting       1111 1111 1111 1111 1111 1111 1100 1000  the int      amp     0000 0000 0000 0000 0000 0000 1111 1111  the 0xFF                                                0000 0000 0000 0000 0000 0000 1100 1000  200      System out println b  amp  0xFF       200         You would typically do this  within  the method that expected an     unsigned byte and the advantage is you apply  0xFF  only once    and than you use the  unsignedByte  variable in all your bitwise    operations        You could use any integer type longer than  byte  for the  unsignedByte  variable     i e   short    int    long  and even  char   but during bitwise operations    it would get casted to  int  anyway      void printUnsignedByte byte b        int unsignedByte   b  amp  0xFF      System out println unsignedByte       200

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If you want unsigned bytes in Java  just subtract 256 from the number you re interested in  It will produce two s complement with a negative value  which is the desired number in unsigned bytes   Example   int speed   255    Integer with the desired byte value byte speed unsigned    byte  speed-256     This will be represented in two s complement so its binary value will be 1111 1111   which is the unsigned byte we desire    You need to use such dirty hacks when using leJOS to program the NXT brick

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A side note  if you want to print it out  you can just say  byte b   255  System out println  b  lt  0   256   b   b

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You can also   public static int unsignedToBytes byte a        return  int      a  lt  lt  24   gt  gt  gt  24           Explanation    let s say a    byte  133   In memory it s stored as   1000 0101   0x85 in hex   So its representation translates  unsigned 133  signed -123  as 2 s complement      a  lt  lt  24    When left shift is performed 24 bits to the left  the result is now a 4 byte integer which is represented as     10000101 00000000 00000000 00000000   or  0x85000000  in hex   then we have        a  lt  lt  24      24   and it shifts again on the right 24 bits but fills with leading zeros  So it results to    00000000 00000000 00000000 10000101   or  0x00000085  in hex   and that is the unsigned representation which equals to 133   If you tried to cast a    int  a  then what would happen is it keeps the 2 s complement representation of byte and stores it as int also as 2 s complement    int   10000101  ---   11111111 11111111 11111111 10000101   And that translates as  -123

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Complete guide for working with unsigned bytes in Java  Unsigned byte in Java  Source for this answer    The Java Language does not provide anything like the unsigned keyword  A byte according to the language spec represents a value between -128 - 127  For instance  if a byte is cast to an int Java will interpret the first bit as the sign and use sign extension  That being said  nothing prevents you from viewing a byte simply as 8 bits and interpret those bits as a value between 0 and 255  Just keep in mind that there s nothing you can do to force your interpretation upon someone else s method  If a method accepts a byte  then that method accepts a value between -128 and 127 unless explicitly stated otherwise  Here are a couple of useful conversions   manipulations for your convenience  Conversions to   from int    From int to unsigned byte int i   200                        some value between 0 and 255 byte b    byte  i                  8 bits representing that value      From unsigned byte to int byte b   123                       8 bits representing a value between 0 and 255 int i   b  amp  0xFF                   an int representing the same value   Or  if you re on Java 8   use Byte toUnsignedInt   Parsing   formatting Best way is to use the above conversions     Parse an unsigned byte byte b    byte  Integer parseInt  quot 200 quot         Print an unsigned byte System out println  quot Value of my unsigned byte   quot     b  amp  0xFF     Arithmetics The 2-complement representation  quot just works quot  for addition  subtraction and multiplication     two unsigned bytes byte b1    byte  200  byte b2    byte  15   byte sum     byte   b1   b2       215 byte diff    byte   b1 - b2       185 byte prod    byte   b2   b2       225  Division requires manual conversion of operands  byte ratio    byte    b1  amp  0xFF     b2  amp  0xFF

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Yes and no  Ive been digging around with this problem   Like i understand this    The fact is that java has signed interger -128 to 127   It is possible to present a unsigned in java with    public static int toUnsignedInt byte x        return   int  x   amp  0xff      If you for example add -12 signed number to be unsigned you get 244  But you can use that number again in signed  it has to be shifted back to signed and it  ll be again -12    If you try to add 244 to java byte you ll get outOfIndexException   Cheers

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I m not sure I understand your question  I just tried this and for byte -12  signed value  it returned integer 244  equivalent to unsigned byte value but typed as an int     public static int unsignedToBytes byte b        return b  amp  0xFF         public static void main String   args        System out println unsignedToBytes  byte  -12         Is it what you want to do  Java does not allow to express 244 as a byte value  as would C  To express positive integers above Byte MAX VALUE  127  you have to use a different integral type  like short  int or long

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Although it may seem annoying  coming from C  that Java did not include unsigned byte in the language it really is no big deal since a simple  b  amp  0xFF  operation yields the unsigned value for  signed  byte b in the  rare  situations that it is actually needed  The bits don t actually change -- just the interpretation  which is important only when doing for example some math operations on the values

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There is no unsigned byte in Java  but if you want to display a byte  you can do   int myInt   144   byte myByte    byte  myInt   char myChar    char   myByte  amp  0xFF    System out println  myChar      Integer toHexString myChar      Output   myChar   90   For more information  please check  How to display a hex byte value in Java

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If think you are looking for something like this   public static char toUnsigned byte b        return  char   b  gt   0   b   256   b

[java] Can we make unsigned byte in Java

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