java date退后一个月 java当前日期减一个月

SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
		Date endDate=new Date();
		System.out.println(sdf.format(endDate)+"=================");
		Calendar date=Calendar.getInstance();
		date.setTime(endDate);
		date.set(Calendar.MONTH, date.get(Calendar.MONTH)-1);
		Date startDate=null;
		try {
			startDate = sdf.parse(sdf.format(date.getTime()));
		} catch (ParseException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}