Question

To read/write binary files, I am using DataInputStream/DataOutputStream, they have this method writeByte()/readByte(), but what I want to do is read/write bits? Is it possible?

I want to use it for a compression algorithm, so when I am compressing I want to write 3 bits(for one number and there are millions of such numbers in a file) and if I write a byte at everytime I need to write 3 bits, I will write loads of redundant data…

Answer 1

It’s not possible to read/write individual bits directly, the smallest unit you can read/write is a byte.

You can use the standard bitwise operators to manipulate a byte though, so e.g. to get the lowest 2 bits of a byte, you’d do

byte b = in.readByte();
byte lowBits = b&0x3;

set the low 4 bits to 1, and write the byte:

b |= 0xf;
out.writeByte(b);

(Note, for the sake of efficiency you might want to read/write byte arrays and not single bytes)