java中 日期增加指定天数

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
Date date=new Date();
String dateFormat1=sdf.format(date);
System.out.println(dateFormat1);
System.out.println(date);
Calendar calendar=Calendar.getInstance();
calendar.setTime(date);
calendar.add(Calendar.DATE, 4);
Date date2=calendar.getTime();
System.out.println(date2);	
String dateFormat=sdf.format(date2);
System.out.println(dateFormat);