code: public void stop() throws IllegalStateException {
  		if (!this.running) {
  			throw new IllegalStateException("Can't stop StopWatch: it's not running");
  		}
  		long lastTime = System.currentTimeMillis() - this.startTimeMillis;
  		this.totalTimeMillis += lastTime;
  		this.lastTaskInfo = new TaskInfo(this.currentTaskName, lastTime);
  		if (this.keepTaskList) {
  			this.taskList.add(lastTaskInfo);
  		}
  		++this.taskCount;
  		this.running = false;
  		this.currentTaskName = null;
  	}
docs: Stop the current task. The results are undefined if timing methods are
  called without invoking at least one pair {@link #start()} /
  {@link #stop()} methods.
  
  @see #start()