Convert string Date into timestamp in Android?

I want to convert my date (which is in String format), e.g. 13-09-2011, into Timestamp. I used below code but I got the 2011-09-13 00:00:00.0 as a result. But I want Timestamp like,1312828200000 format.

I cannot understand how to convert that.

My code:

String str_date="13-09-2011";
DateFormat formatter ; 
Date date ; 
formatter = new SimpleDateFormat("dd-MM-yyyy");
date = (Date)formatter.parse(str_date); 
java.sql.Timestamp timeStampDate = new Timestamp(date.getTime());
System.out.println("Today is " +timeStampDate);