Android : Get interval date in Android?

I want interval date. Whatever user enter date from date picker and from this date I want to get after one month date Suppose 1 Aug 2014 -> Output will be 1 September 2014.Can someone help me .Thanks to appreciate.

Hare is my Activity code

{
// Get current date by calender
         final Calendar c = Calendar.getInstance();
         year  = c.get(Calendar.YEAR);
         month = c.get(Calendar.MONTH);
         day   = c.get(Calendar.DAY_OF_MONTH);

        // Month is 0 based, just add 1
         etReplacementDate.setText(new StringBuilder()
        .append(month + 1).append("-").append(day).append("-")
        .append(year).append(" "));

         etReplacementDate.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                showDialog(DATE_OF_REPLACEMENT);
            }
        });

         String fixedDate = etReplacementDate.getText().toString().trim();

         SimpleDateFormat dateFormat = new SimpleDateFormat("MM/dd/yyyy hh:mm:ss aa");
            Date convertedDate = new Date();
            try
            {
                convertedDate = dateFormat.parse(fixedDate);
            }
            catch (ParseException e) 
            {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            System.out.println("Date Consersion  = " + convertedDate);


     /****************ReplaceMent Date***************************************************/
         cal2.add(Calendar.getInstance(convertedDate), 30);
         Date date_30dayslater = cal2.getTime();
         System.out.println("date_30dayslater : " + date_30dayslater);


         /****************Interval Date***************************************************/
         String _30daysLater_String = new SimpleDateFormat("yyyy-MM-dd").format(date_30dayslater);
         etNextReplanishmentDate.setText(_30daysLater_String);
         System.out.println("30 days later: " + _30daysLater_String);
         System.out.println("______________________________________");

/****************Before Date***************************************************/
         cal2.add(Calendar.DATE, -1);
         Date beforDate = cal2.getTime();
         String beforDate_String = new SimpleDateFormat("yyyy-MM-dd").format(beforDate);
         System.out.println("beforDate_String: " + beforDate_String);     
}


@Override 
    protected Dialog onCreateDialog(int id)
    {
        switch (id) 
        {
        case DATE_OF_REPLACEMENT:return new DatePickerDialog(this, pickerListenerReplacement, year, month, day);
        }
        return null;
    }


    private DatePickerDialog.OnDateSetListener pickerListenerReplacement = new DatePickerDialog.OnDateSetListener() {

        // when dialog box is closed, below method will be called.
        @Override
        public void onDateSet(DatePicker view, int selectedYear,
                int selectedMonth, int selectedDay) {

            year  = selectedYear;
            month = selectedMonth;
            day   = selectedDay;

            // Show selected date 
            etReplacementDate.setText(new StringBuilder().append(month + 1)
                    .append("-").append(day).append("-").append(year)
                    .append(" "));

           }
        };
        }