public void stop() {
		if (this.runningState != STATE_RUNNING
				&& this.runningState != STATE_SUSPENDED) {
			throw new IllegalStateException("Stopwatch is not running. ");
		}
		if (this.runningState == STATE_RUNNING) {
			this.stopTime = System.currentTimeMillis();
		}
		this.runningState = STATE_STOPPED;
	}