/** A simple millisecond stopwatch.  
 * start() sets stopwatch measure of time elapsed.
 * stop() adds time elapsed since previous start() to total elapsed time and returns total elapsed time.
 * reset() resets total elapsed time.
 * lap() returns total elapsed time without "stopping" the stopwatch.
 * It's actually easier to read the code than these comments. :)
 */

public class Stopwatch {
    private long totalMillis = 0;
    private long startMillis = 0;
    private long stopMillis = 0;

    /**
     * Return millisecond stopwatch time elapsed so far.
     * @return long
     */
    public long lap() {
	return (System.currentTimeMillis() - startMillis) + totalMillis;
    }

    /**
     * Reset the millisecond stopwatch.
     */
    public void reset() {
	totalMillis = startMillis = stopMillis = 0; 
    }

    /**
     * Start millisecond stopwatch.
     */
    public void start() {
	startMillis = System.currentTimeMillis();
    }

    /**
     * Stop millisecond stopwatch and return total time elapsed.
     * @return long
     */
    public long stop() {
	stopMillis = System.currentTimeMillis();
	totalMillis += stopMillis - startMillis;
	startMillis = stopMillis = 0;
	return totalMillis;
    }

}