public long diff(){
  if (running)   return System.currentTimeMillis() - startTime;
 else   return stopTime - startTime;
}

public long diff ( ) { if ( running ) return System . currentTimeMillis ( ) - startTime ; else return stopTime - startTime ; }
return the number of milliseconds the timer has been running . ( up till now , if it still runs , up to the stop time if it has been stopped )
