/**
 A class to measure time elapsed.
*/

public class Stopwatch
{
    private long startTime;
    private long stopTime;

    public static final double NANOS_PER_SEC = 1000000000.0;

    /**
     start the stop watch
    */
    public void start()
    {  
        startTime = System.nanoTime();
    }

    /**
     stop the stop watch
    */
    public void stop()
    {   stopTime = System.nanoTime();   }

    /**
    elapsed time in secods
    @return the time recorded on the stopwatch in seconds
    */
    public double time()
    {   return (stopTime - startTime) / NANOS_PER_SEC;  }

    public String toString()
    {   return "elapsed time: " + time() + " seconds.";
    }

    /**
    elapsed time in nanoseconds
    @return the time recorded on the stopwatch in milliseconds
    */
    public long timeInNanoseconds()
    {   return (stopTime - startTime);  }
}