Calculating date/time diff

I am quite new to Android development. I need to get the difference(duration) between two data/time values. When I try to get the difference between to date/times I guess the app is crashing. Heres the code:

                 // txtStartDate text = 4/8/2018

                          // txtStartTiem text = 11:16 PM


              // txtEndDate text = 4/8/2018
             // txtEndtime text = 12:30 (0:30 AM)


            String format ="yyyy-MM-dd'T'HH:mm:ss" ;//“yyyy-MM-dd’T’HH:mm:ss”;
                        SimpleDateFormat simpleFormat = new SimpleDateFormat(format);
                        String strStartDateText = txtStartDate.getText().toString() + " " + txtStartTime.getText().toString();
                        Date startDate = simpleFormat.parse(strStartDateText  , new ParsePosition(1));

                        String strEndDateText = txtEndDate.getText().toString() + " " + txtEndTime.getText().toString();
                        Date EndDate = simpleFormat.parse(strEndDateText  , new ParsePosition(1));



                        long different = EndDate.getTime() - startDate.getTime(); // suspected crash.

What could be wrong here?