java date 日期加减天数

测试类代码：

import java.text.SimpleDateFormat;
import java.util.Date;

public class DateTest {

public static void main(String[] arg){
Date now = new Date();

addAndSubtractDaysByGetTime(now,-5);
addAndSubtractDaysByGetTime(now,5);
addAndSubtractDaysByCalendar(now,-5);
addAndSubtractDaysByCalendar(now,5);
}

public static Date addAndSubtractDaysByGetTime(Date dateTime/*待处理的日期*/,int n/*加减天数*/){

//日期格式
SimpleDateFormat df=new SimpleDateFormat("yyyy-MM-dd");
SimpleDateFormat dd=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

System.out.println(df.format(new Date(dateTime.getTime() + n * 24 * 60 * 60 * 1000L)));
//System.out.println(dd.format(new Date(dateTime.getTime() + n * 24 * 60 * 60 * 1000L)));
//注意这里一定要转换成Long类型，要不n超过25时会出现范围溢出，从而得不到想要的日期值
return new Date(dateTime.getTime() + n * 24 * 60 * 60 * 1000L);
}

public static Date addAndSubtractDaysByCalendar(Date dateTime/*待处理的日期*/,int n/*加减天数*/){

//日期格式
SimpleDateFormat df=new SimpleDateFormat("yyyy-MM-dd");
SimpleDateFormat dd=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

java.util.Calendar calstart = java.util.Calendar.getInstance();
calstart.setTime(dateTime);

calstart.add(java.util.Calendar.DAY_OF_WEEK, n);

System.out.println(df.format(calstart.getTime()));
//System.out.println(dd.format(calstart.getTime()));
return calstart.getTime();
}

}

运行结果：
2014-10-06

2014-10-16

2014-10-06

2014-10-16