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() - (long)2 * 24 * 60 * 60 * 1000)));
System.out.println("三天后的日期:" + df.format(new Date(d.getTime() + (long)3 * 24 * 60 * 60 * 1000)));