Question

If I have an integer that I’d like to perform bit manipulation on, how can I load it into a java.util.BitSet? How can I convert it back to an int or long? I’m not so concerned about the size of the BitSet — it will always be 32 or 64 bits long. I’d just like to use the set(), clear(), nextSetBit(), and nextClearBit() methods rather than bitwise operators, but I can’t find an easy way to initialize a bit set with a numeric type.

Answer 1

The following code creates a bit set from a long value and vice versa:

public class Bits {

  public static BitSet convert(long value) {
    BitSet bits = new BitSet();
    int index = 0;
    while (value != 0L) {
      if (value % 2L != 0) {
        bits.set(index);
      }
      ++index;
      value = value >>> 1;
    }
    return bits;
  }

  public static long convert(BitSet bits) {
    long value = 0L;
    for (int i = 0; i < bits.length(); ++i) {
      value += bits.get(i) ? (1L << i) : 0L;
    }
    return value;
  }
}

EDITED: Now both directions, @leftbrain: of cause, you are right