JAVA 日期加减

import java.util.Date;
import java.text.SimpleDateFormat;
import java.util.Calendar;
 
public class DateTest {
 /**
  * @param args
  */
 public static void main(String[] args) throws Exception {
  // TODO 自动生成方法存根
  //日期相减算出秒的算法
  Date date1 = new SimpleDateFormat("yyyy-mm-dd").parse("2005-06-08");
  Date date2 = new SimpleDateFormat("yyyy-mm-dd").parse("2006-06-12");
 
  long l = date1.getTime()-date2.getTime()>0 ? date1.getTime()-date2.getTime():
   date2.getTime()-date1.getTime();
 
  //System.out.println(l/1000+"秒");
 
  //日期相减得到相差的日期
  long day = (date1.getTime()-date2.getTime())/(24*60*60*1000)>0 ? (date1.getTime()-date2.getTime())/(24*60*60*1000):
   (date2.getTime()-date1.getTime())/(24*60*60*1000);
 
  long day1=date1.getTime();
  Date sb = new Date();
  sb.setTime(day1);
  System.out.println(Ds(30));
 // System.out.println("相差的日期: " +day);
 
 }
 
 public static String Ds(int days){
  SimpleDateFormat form=new SimpleDateFormat("yyyy-MM-dd");
  Calendar calendar = Calendar.getInstance();
    int day = calendar.get(Calendar.DAY_OF_YEAR);
    calendar.set(Calendar.DAY_OF_YEAR, day - days);
    Date cc = calendar.getTime();
    return form.format(cc);
 }
}