java 对日期的处理

 private static String getString(Date date){

            SimpleDateFormat sf = new SimpleDateFormat("yyyy-MM-dd");
            String str=sf.format(date);
            return str;
        }
     private static String getString(){
         Date date =new Date();
            SimpleDateFormat sf = new SimpleDateFormat("yyyy-MM-dd");
            String str=sf.format(date);
            return str;
        }
        private static String getStringdatil(){
            Date date=new Date();
            SimpleDateFormat sf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
            String str=sf.format(date);
            return str;
        }
        private static Date getshangMonth(){
             Calendar calendar = Calendar.getInstance();
             Date date=new Date();
             calendar.setTime(date);
             calendar.add(Calendar.MONTH, -1);

             return calendar.getTime();
        }
        private static Date getshangDay(){
             Calendar calendar = Calendar.getInstance();
             Date date=new Date();
             calendar.setTime(date);
             calendar.add(Calendar.DAY_OF_MONTH, -1);
             return calendar.getTime();
        }
        private static Date getshangDay(Date date){
             Calendar calendar = Calendar.getInstance();

             calendar.setTime(date);
             calendar.add(Calendar.DAY_OF_MONTH, -1);
             return calendar.getTime();
        }
        private static Date getshangYear(){
             Calendar calendar = Calendar.getInstance();
             Date date=new Date();
             calendar.setTime(date);
             calendar.add(Calendar.YEAR, -1);

             return calendar.getTime();
        }