public VM_Address next() { VM_Address rv = hasNext_ ? bitmapToAddress(iterPage_, iterSlot_, iterWord_, iterBit_) : VM_Address.zero(); advanceIterator(true); return rv; }
public VM_Address next() { return null; }
  public VM_Address next() {    VM_Address rv = hasNext_ ? bitmapToAddress(iterPage_, iterSlot_, iterWord_, iterBit_)                              : VM_Address.zero();    advanceIterator(true);    return rv;  }