求助!关于Calendar类的问题
public   class   TestCalendar   {
        public   static   void   main(String[]   args){
                Calendar   cl=Calendar.getInstance();
  System.out.print(cl.get(Calendar.YEAR)+ "年 "   +cl.get(Calendar.MONTH)+ "月 "+   cl.get(Calendar.DAY_OF_MONTH)+ "日 "+ "     ");
System.out.print( "星期 "+cl.get(Calendar.DAY_OF_WEEK_IN_MONTH)+ "     ");
System.out.println( "21天以后是： ");
        cl.add(Calendar.DAY_OF_YEAR,21);
System.out.print(cl.get(Calendar.YEAR)+ "年 "   +cl.get(Calendar.MONTH)+ "月 "   +   cl.get(Calendar.DAY_OF_MONTH)+ "日 "+ "     ");
                System.out.print( "星期 "+cl.get(Calendar.DAY_OF_WEEK_IN_MONTH)+ "     ");
    }
}  
这是我的一段代码   结果是
                                                2007年0月17日     星期3    
                                                21天以后是：
                                                2007年1月7日     星期1  
后来我把       cl.get(Calendar.MONTH)   改成了   (cl.get(Calendar.MONTH)+1)   结果月份是对了     但是星期还是有问题         加了21天     应该还是星期3啊
后来的结果是  
2007年1月17日     星期3    
21天以后是：
2007年2月7日     星期1    


(我的系统时间是2007年1月17日星期3)

麻烦各位指教,谢谢了


------解决方案--------------------
楼主对 DAY_OF_WEEK_IN_MONTH 的理解有误，楼主应该用 DAY_OF_WEEK。先照抄 JDK 文档如下：
public static final int DAY_OF_WEEK_IN_MONTH = 8
Field number for get and set indicating the ordinal number of the day of the week within the current month. Together with the DAY_OF_WEEK field, this uniquely specifies a day within a month. Unlike WEEK_OF_MONTH and WEEK_OF_YEAR, this field 's value does not depend on getFirstDayOfWeek() or getMinimalDaysInFirstWeek(). DAY_OF_MONTH 1 through 7 always correspond to DAY_OF_WEEK_IN_MONTH 1; 8 through 14 correspond to DAY_OF_WEEK_IN_MONTH 2, and so on. DAY_OF_WEEK_IN_MONTH 0 indicates the week before DAY_OF_WEEK_IN_MONTH 1. Negative values count back from the end of the month, so the last Sunday of a month is specified as DAY_OF_WEEK = SUNDAY, DAY_OF_WEEK_IN_MONTH = -1. Because negative values count backward they will usually be aligned differently within the month than positive values. For example, if a month has 31 days, DAY_OF_WEEK_IN_MONTH -1 will overlap DAY_OF_WEEK_IN_MONTH 5 and the end of 4.

懂了没？每月1～7号，DAY_OF_WEEK_IN_MONTH 为 1；8~14号，DAY_OF_WEEK_IN_MONTH 为 2，依此类推。

------解决方案--------------------
Calendar.DAY_OF_WEEK_IN_MONTH=====〉DAY_OF_WEEK