1.用Java.util.Calender来实现

   Calendar calendar=Calendar.getInstance();   
   calendar.setTime(new Date()); 
   System.out.println(calendar.get(Calendar.DAY_OF_MONTH));//今天的日期 
   calendar.set(Calendar.DAY_OF_MONTH,calendar.get(Calendar.DAY_OF_MONTH)+3);//日期加3
   System.out.println(calendar.get(Calendar.DATE));//加3之后的日期 
 

2.用java.text.SimpleDateFormat和java.util.Date来实现
           
    Date d=new Date();   
   SimpleDateFormat df=new SimpleDateFormat("yyyy-MM-dd");   
   System.out.println("今天的日期："+df.format(d));   
   System.out.println("两天前的日期：" + df.format(new Date(d.getTime() - 2 * 24 * 60 * 60 * 1000)));  
   System.out.println("三天后的日期：" + df.format(new Date(d.getTime() + 3 * 24 * 60 * 60 * 1000)));