Java BitSet which allows easy Concatenation of BitSets

Question

I have a need for a BitSet which allows easy concatenation of multiple BitSets create a new BitSet. The default implementation doesn't have such a method.

Is there any an implementation in some external library that any of you know which allows easy concatenation?

For example lets say I have a bitarray 11111 and another bit array 010101. I want functionality like appending. So after concatenating it would result in 11111010101.

Answer 1

Well there's no way to implement this terribly efficient (performance and memory that is) since there's no leftshift method.

What you can do is either use the obvious nextSetBit for loop - slow, but memory efficient.

The presumably faster method would be to use toLongArray on one, copy that correctly shifted into a large enough array, create a bitset from that and or it with the other. That way you don't do any bitshifting on single bits but instead work on wordsized chunks.

Answer 2

This worked for me:

BitSet concatenate_vectors(BitSet vector_1_in, BitSet vector_2_in) {
  BitSet vector_1_in_clone = (BitSet)vector_1_in.clone();
  BitSet vector_2_in_clone = (BitSet)vector_2_in.clone();
  int n = 5;//_desired length of the first (leading) vector
  int index = -1;
  while (index < (vector_2_in_clone.length() - 1)) {
    index = vector_2_in_clone.nextSetBit((index + 1));
    vector_1_in_clone.set((index + n));
  }
  return vector_1_in_clone;
}

Result: 11111010101