Set specific bit in byte

80
votes

I'm trying to set bits in Java byte variable. It does provide propper methods like .setBit(i). Does anybody know how I can realize this?

I can iterate bit-wise through a given byte:

if( (my_byte & (1 << i)) == 0 ){

}

However I cannot set this position to 1 or 0, can I?

5
javabytebit-manipulation
Possible duplicate of How do you set, clear, and toggle a single bit? - phuclv
@phuclv That is a C/C++ question, not a Java question. - Mark Rotteveel
@MarkRotteveel the same syntax is used. If fact the tag should be renamed to something like C-like - phuclv
@phuclv The fact it uses the same syntax is - in my opinion - not a sufficient reason to close as duplicate. - Mark Rotteveel

5 Answers

147
votes

Use the bitwise OR (|) and AND (&) operators. To set a bit, namely turn the bit at pos to 1:

my_byte = my_byte | (1 << pos);   // longer version, or
my_byte |= 1 << pos;              // shorthand

To un-set a bit, or turn it to 0:

my_byte = my_byte & ~(1 << pos);  // longer version, or
my_byte &= ~(1 << pos);           // shorthand

For examples, see Advanced Java/Bitwise Operators

70
votes

To set a bit:

myByte |= 1 << bit;

To clear it:

myByte &= ~(1 << bit);
28
votes

Just to complement Jon‘s answer and driis‘ answer

To toggle (invert) a bit 

    myByte ^= 1 << bit;
12
votes

The technique you need is to isolate the chosen bit and either set or clear it. You already have the expression to isolate the bit since you're using that to test it above. You can set the bit by ORing it in, or clear the bit by bitwise AND with the 1's complement of the bit.

boolean setBit;
my_byte = setBit
          ? myByte | (1 << i)
          : myByte & ~(1 << i);
8
votes

Please see the class java.util.BitSet that do the job for you.

To set : myByte.set(bit); To reset : myByte.clear(bit); To fill with a bool : myByte.set(bit, b); To get the bool : b = myByte.get(bit); Get the bitmap : byte bitMap = myByte.toByteArray()[0];