java.util.BitSet#previousClearBit ( )源码实例Demo

/**
 * Given a BitSet, returns a random bit that is currently false, or -1 if all bits are true.
 * NOTE: this method is not fair.
 */
public static final int randomUnsetBit(Random r, BitSet bits, final int max) {
  // NOTE: don't forget, BitSet will grow automatically if not careful
  if (bits.cardinality() == max+1) {
    return -1;
  }
  final int candidate = TestUtil.nextInt(r, 0, max);
  if (bits.get(candidate)) {
    final int lo = bits.previousClearBit(candidate);
    final int hi = bits.nextClearBit(candidate);
    if (lo < 0 && max < hi) {
      fail("how the hell did we not short circut out? card="+bits.cardinality()+"/size="+bits.size());
    } else if (lo < 0) {
      return hi;
    } else if (max < hi) {
      return lo;
    } // else...
    return ((candidate - lo) < (hi - candidate)) ? lo : hi;
  }
  return candidate;
}
 

@Override
public Range<T> rangeContaining(long key, long value) {
    BitSet rangeBitSet = rangeBitSetMap.get(key);
    if (rangeBitSet != null) {
        if (!rangeBitSet.get(getSafeEntry(value))) {
            // if position is not part of any range then return null
            return null;
        }
        int lowerValue = rangeBitSet.previousClearBit(getSafeEntry(value)) + 1;
        final T lower = consumer.apply(key, lowerValue);
        final T upper = consumer.apply(key,
                Math.max(rangeBitSet.nextClearBit(getSafeEntry(value)) - 1, lowerValue));
        return Range.closed(lower, upper);
    }
    return null;
}