java獲取指定日期的前幾天時間

Calendar cal = Calendar.getInstance();
cal.set(2019,10,11);
Date time = cal.getTime();
System.out.println("當前指定日期是："+new SimpleDateFormat(fm).format(time));
cal.add(Calendar.DAY_OF_MONTH,-2);
cal.getTime();
System.out.println("前兩天的日期是 "+new SimpleDateFormat(fm).format(cal.getTime()));