What does value 0xff do in Java

Question

I have the following Java code   byte value   0xfe     corresponds to -2  signed  and 254  unsigned  int result   value  amp  0xff    The result is 254 when printed  but I have no idea how this code works  If the  amp  operator is simply bitwise  then why does it not result in a byte and instead an integer

User · Answer

In 32 bit format system the hexadecimal value 0xff represents 00000000000000000000000011111111 that is 255 15 16 1 15 16 0  in decimal  and the bitwise  amp  operator masks the same 8 right most bits as in first operand

User · Answer

It help to reduce lot of codes  It is occasionally used in RGB values which consist of 8bits    where 0xff means  24 0 s    and 8 1 s  like 00000000 00000000 00000000 11111111      It effectively masks the variable so it leaves only the value in the last 8 bits  and ignores all the rest of the bits   It   s seen most in cases like when trying to transform color values from a special format to standard RGB values  which is 8 bits long    Great Explanation See here

User · Answer

It sets result to the  unsigned  value resulting from putting the 8 bits of value in the lowest 8 bits of result   The reason something like this is necessary is that byte is a signed type in Java  If you just wrote   int result   value    then result would end up with the value ff ff ff fe instead of 00 00 00 fe  A further subtlety is that the  amp  is defined to operate only on int values1  so what happens is    value is promoted to an int  ff ff ff fe   0xff is an int literal  00 00 00 ff   The  amp  is applied to yield the desired value for result     The point is that conversion to int happens before the  amp  operator is applied    1Well  not quite  The  amp  operator works on long values as well  if either operand is a long  But not on byte  See the Java Language Specification  sections 15 22 1 and 5 6 2

User · Answer

From http   www coderanch com t 236675 java-programmer-SCJP certification xff  The hex literal 0xFF is an equal int 255   Java represents int as 32 bits  It look like this in binary   00000000 00000000 00000000 11111111   When you do a bit wise AND with this value 255  on any number  it is going to mask make ZEROs  all but the lowest 8 bits of the number  will be as-is        01100100 00000101  amp     00000000 11111111   00000000 00000101    amp  is something like   but not really   And why 0xff  this in   power of 2  - 1   All   power of 2  - 1   e g 7  255     will behave something like   operator   Then In binary  0 is  all zeros  and 255 looks like this   00000000 00000000 00000000 11111111   And -1 looks like this  11111111 11111111 11111111 11111111   When you do a bitwise AND of 0xFF and any value from 0 to 255  the result is the exact same as the value  And if any value higher than 255 still the result will be within 0-255   However  if you do   -1  amp  0xFF   you get  00000000 00000000 00000000 11111111  which does NOT equal the original value of -1  11111111 is 255 in decimal         Few more bit manipulation   Not related to the question    X  gt  gt  1   X 2 X  lt  lt  1   2X   Check any particular bit is set 1  or not  0  then   int thirdBitTobeChecked     1  lt  lt  2       0000100   int onWhichThisHasTobeTested   5             101    int isBitSet   onWhichThisHasTobeTested   amp  thirdBitTobeChecked   if isBitSet  gt  0        Third Bit is set to 1        Set 1  a particular bit   int thirdBitTobeSet     1  lt  lt  2        0000100   int onWhichThisHasTobeSet   2             010   onWhichThisHasTobeSet    thirdBitTobeSet    ReSet 0  a particular bit  int thirdBitTobeReSet       1  lt  lt  2           1111011  int onWhichThisHasTobeReSet   6               000110  onWhichThisHasTobeReSet  amp   thirdBitTobeReSet    XOR       Just note that if you perform XOR operation twice  will results the same value   byte toBeEncrypted   0010 0110 byte salt            0100 1011  byte encryptedVal     toBeEncrypted   salt    0110 1101 byte decryptedVal     encryptedVal    salt    0010 0110    toBeEncrypted      One more logic with XOR is  if     A  XOR  B    C  salt  then   C  XOR  B    A        C  XOR  A    B   The above is useful to swap two variables without temp like below  a   a   b  b   a   b  a   a   b    OR  a    b    a    b

[java] What does value & 0xff do in Java?

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