How to calculate difference of date and time in Java

To calculate date and time difference with manual calculation...

• Very first step to convert date into milliseconds (ms)
• String date1 = "01-02-2015 09:15:20";
• SimpleDateFormat format = new  SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
• HH convert into 24 hours format (0-23)
• hh convert into 12 hours format
•  Date d1 = format.parse(date1);
• long ms = d1.getTime();