23/02/2018

[Java] Set a specific bit in a byte type

First of all let's start by saying that quite counter intuitively, Boolean in Java is not a single bit but either a 32 or 64 bit entity while a boolean[] uses a byte for each element :)

Now that the shock is passed, let's see how to set a specific bit in a byte object:

 public void set(int bit){  
  byte b = (byte)(1 << (bit - 1));  
  res |= b;  
 }  


Assuming res is our byte variable. And yes, the cast is there since the shift operation << returns an int, therefore it must be cast back to byte type, otherwise the bitwise OR would later fail!

And the -1 is of course because we start with position 0 on the right. Note that using the bitwise OR will set the bit ONCE and never revert it back!

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