编写日历代码的问题，求讲解

Question

请求前辈讲解一下下面的代码，不停地set （day_of_month,1）是为什么呢？代码不太看的懂，希望有人能讲解一下，谢谢了： import java.util.Calendar; import java.util.Date; import java.util.GregorianCalendar; import java.text.DateFormat; import java.text.DateFormatSymbols; import java.text.ParseException; import java.text.SimpleDateFormat; public class T2{ public static void main(String[] args) throws ParseException{ Date date=new Date(); DateFormat format=new SimpleDateFormat("yyyy年MM月dd日HH时mm分ss秒"); System.out.println("北京时间："+format.format(date)); Calendar cal=Calendar.getInstance(); int year=cal.get(Calendar.YEAR); int month=cal.get(Calendar.MONTH); int today = cal.get(Calendar.DAY_OF_MONTH); int count=0; //cal.set(Calendar.DAY_OF_MONTH, ); //System.out.println(cal.get(Calendar.DAY_OF_MONTH)); cal.set(Calendar.DAY_OF_MONTH,1); int week = cal.get(Calendar.DAY_OF_WEEK); //System.out.println(cal.get(Calendar.DAY_OF_WEEK)); int firstDayOfWeek = cal.getFirstDayOfWeek(); while(firstDayOfWeek != week){ ++count; cal.add(Calendar.DAY_OF_MONTH, -1); week = cal.get(Calendar.DAY_OF_WEEK); } String[] weeks = { "日", "一", "二", "三", "四", "五", "六" }; for(String w:weeks){ System.err.print(w+" "); } do{ cal.add(Calendar.DAY_OF_MONTH, 1); week = cal.get(Calendar.DAY_OF_WEEK); }while(week != firstDayOfWeek); System.out.println(); for(int i = 0;i < count;++i){ System.out.print(" "); } cal.set(Calendar.DAY_OF_MONTH, 1); week = cal.get(Calendar.DAY_OF_WEEK); int day = cal.get(Calendar.DAY_OF_MONTH); //System.out.println(day); do{ System.out.printf("%2s",day); if(today == day){ System.out.print("*"); }else{ System.out.print(" "); } cal.add(Calendar.DAY_OF_MONTH,1 ); week = cal.get(Calendar.DAY_OF_WEEK); day = cal.get(Calendar.DAY_OF_MONTH); if(week == firstDayOfWeek){ System.out.println(); } }while(month == cal.get(Calendar.MONTH)); if(week != firstDayOfWeek){ System.out.println(); } } }