The following code might be helpful:
public static void main(String[] args)
      {
            Scanner reader = new Scanner(System.in); 
            System.out.println("Enter two dates and time in the following format (yy/MM/dd HH:mm:ss) : ");
            String dateStart = reader.nextLine();
            String dateStop = reader.nextLine();
            reader.close();
           SimpleDateFormat format = new SimpleDateFormat("yy/MM/dd HH:mm:ss");
           java.util.Date d1 = null;
           java.util.Date d2 = null;
           try
          {
                  d1 =  format.parse(dateStart);
           }
          catch (java.text.ParseException e)
          {
                  e.printStackTrace();
           }
           try
           {
                  d2 =  format.parse(dateStop);
           }
           catch (java.text.ParseException e)
           {
                  e.printStackTrace();
           }
           long d = d2.getTime() - d1.getTime();
           long dS = d / 1000 % 60;
           long dM = d / (60 * 1000) % 60;
           long dH = d / (60 * 60 * 1000);
           long days=0;
           if (dH>24)
           {
            days = dH/24;
            dH = dH - (24*days);
          }
          System.out.println("The elapsed time is: "+days+" Days "+dH+" Hours "+dM+ " Minutes "+dS+" Seconds ");       
      }
}