How to calculate the size of a BitSet in bytes?

Question

I used a Java BitSet to encode a message.

My compressed file size comes out to 954kb, but when I do BitSet.cardinality() , I get around 4mb. Can you explain this?

Answer 1

BitSet.cardinality() returns the number of bits set to true in the BitSet . I think you are looking for BitSet.size() . But keep in mind it will return the number of bits , not bytes .

Assuming after Huffman encoding you have approximately half of the bits set to true , that means your BitSet should have a size of around 4.000.000*2 = 8.000.000 bits in your BitSet which in turn makes around 1.000.000 bytes which is rather close to the 954kb you see.

This should explain your observation.