private void writeObject(java.io.ObjectOutputStream s) throws IOException  {
    s.defaultWriteObject();     // Nothing to write
    final NBSI nbsi = _nbsi;    // The One Field is transient
    final int len = _nbsi._bits.length<<6;
    s.writeInt(len);            // Write max element
    for( int i=0; i<len; i++ )
      s.writeBoolean( _nbsi.contains(i) );
  }
Standard Java {@link Iterator}.  Not very efficient because it
auto-boxes the returned values.
jctools-core/src/main/java/org/jctools/maps/NonBlockingSetInt.java