@Override public boolean isModified(){
  long now=CurrentTime.currentTime();
  long lastCheckTime=_lastCheckTime.get();
  if (now <= lastCheckTime + _checkInterval) {
    return _isModified;
  }
  if (!_lastCheckTime.compareAndSet(lastCheckTime,now)) {
    return _isModified;
  }
  if (isModifiedImpl()) {
    _isModified=true;
  }
 else {
    _isModified=false;
  }
  return _isModified;
}

@ Override public boolean isModified ( ) { long now = CurrentTime . currentTime ( ) ; long lastCheckTime = _lastCheckTime . get ( ) ; if ( now <= lastCheckTime + _checkInterval ) { return _isModified ; } if ( ! _lastCheckTime . compareAndSet ( lastCheckTime , now ) ) { return _isModified ; } if ( isModifiedImpl ( ) ) { _isModified = true ; } else { _isModified = false ; } return _isModified ; }
returns true if the underlying resource has changed . xxx : restore ismodified ( ) with
