时间 加 或 减 问题

 

GregorianCalendar   now =new   GregorianCalendar();		
  SimpleDateFormat   fmtrq   =   new   SimpleDateFormat("yyyy-MM-dd");   //"yyyy年MM月dd日",Locale.US
 DateFormat   df   =   DateFormat.getDateInstance();   
System.out.println(fmtrq.format(now.getTime()));   
now.add(GregorianCalendar.MONTH,-1);   
 System.out.println(fmtrq.format(now.getTime()));   
 String str=fmtrq.format(now.getTime());

                Date now=new Date();
            SimpleDateFormat sd=new SimpleDateFormat("yyyy-MM-dd");              
           System.out.println(sd.format(now));
            String myString = DateFormat.getDateInstance().format(now);