public static void main(String[] args){
 
  ElapsedTime elapsedTime = new ElapsedTime();
 
  elapsedTime.start();
 
  // Do some work.
 
  elapsedTime.stop();
 
  elapsedTime.display();
}

Start at 2019-02-27 19:08:43.0032
End   at 2019-02-27 19:08:43.0062
Ran  for 00:00:00.30

package net.openwritings.java.time;
 
import java.util.Calendar;
import java.util.Date;
import java.text.SimpleDateFormat;
 
public class ElapsedTime 
{
  private Calendar startTime = null;
  private Calendar endTime   = null;
 
 
  public ElapsedTime(){}
 
  public void start()
  {
    this.startTime = Calendar.getInstance();
  }
 
  public void setStart(final Calendar calendar)
  {
    this.startTime = calendar;
  }
 
  public void stop()
  {
    this.endTime = Calendar.getInstance();
  }
 
  public void setStop(final Calendar calendar)
  {
    this.endTime = calendar;
  }
 
  /**
   * @return Return the elapsed time measured in milliseconds.
   */
  public final long getDiffInMillis()
  {
    return this.endTime.getTimeInMillis() - this.startTime.getTimeInMillis();
  }
 
  /**
   * @return Return the elapsed time measured as HH:MM:SS.mmmm.
   */
  public final String getDiffInString()
  {
 
    long lTotalRuntime = this.getDiffInMillis();
    long lRuntime      = lTotalRuntime;
 
    // Calculate hours, minutes and seconds.     
    long lRuntimeHrs = lRuntime/(1000*3600);
    lRuntime         = lRuntime - (lRuntimeHrs*1000*3600);// Runtime remaining.
    long lRuntimeMin = (lRuntime)/(1000*60);
    lRuntime         = lRuntime - (lRuntimeMin*1000*60);  // Runtime remaining.
    long lRuntimeSec = lRuntime/(1000);
    lRuntime         = lRuntime - (lRuntimeSec*1000);     // Runtime remaining.
 
    return String.format("%02d", lRuntimeHrs)+":"+String.format("%02d", lRuntimeMin)
                                +":"+String.format("%02d", lRuntimeSec)+"."+lRuntime;
  }
 
  public void display()
  {
    // Start at YYYY-MM-DD HH:MM:SS.mmm
    System.out.println(String.format("Start at %s", this.getDateTimeFormatted(this.startTime)));
 
    // End at YYYY-MM-DD HH:MM:SS.mmm
    System.out.println(String.format("End   at %s", this.getDateTimeFormatted(this.endTime)));
 
    // Ran for HH:MM:SS.mmm (milliseconds)
    System.out.println(String.format("Ran  for %s", this.getDiffInString()));
 
  }
 
  private final String getDateTimeFormatted(Calendar oCalendar)
  {
    final String dateFormat = "yyyy-MM-dd HH:mm:ss.SSSS";
 
    Date currentDate = oCalendar.getTime();
    SimpleDateFormat oSimpleDateFormat = new SimpleDateFormat(dateFormat);
    return oSimpleDateFormat.format(currentDate);
  }
 
  public static void main(String[] args){
 
      ElapsedTime elapsedTime = new ElapsedTime();
 
      elapsedTime.start();
 
      // Do some work.
 
      elapsedTime.stop();
 
      elapsedTime.display();
  }
}