怎么算出今天20141117 一个星期前是20141110 二个星期前是20141103 三个星期前是20141027
------解决思路----------------------
public class CalendarTest {
public static void main(String[] args) throws ParseException {
Date currentD = new Date();
System.out.println("当前时间:"+dateFormat2Str(currentD));
System.out.println("一星期前:"+dateFormat2Str(round(currentD,-7*1)));
System.out.println("两星期前:"+dateFormat2Str(round(currentD,-7*2)));
}
/**
* 得到一个日期的前或后几天,前几天用正整数，后几天用负整数
* @param date
* @param day
* @return
*/
private static Date round(Date date, int day){
Calendar cal = Calendar.getInstance();
cal.setTime(date);
cal.add(Calendar.DATE, day);
return cal.getTime();
}
private static String dateFormat2Str(Date date){
if(date == null){
return null;
}
SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
return sdf.format(date);
}
}