public void stop(){
  if (mState != State.RUNNING) {
    throw new IllegalStateException(mState.toString());
  }
  mTime+=System.nanoTime() - mStart;
  mStart=0;
  mState=State.STOPPED;
}

public void stop ( ) { if ( mState != State . RUNNING ) { throw new IllegalStateException ( mState . toString ( ) ) ; } mTime += System . nanoTime ( ) - mStart ; mStart = 0 ; mState = State . STOPPED ; }
stop clock ticking on current interval and accumulate it into the current time .
