显示日历

## 题目要求 ##
使用MyCalendar 类显示指定月份的日历程序从命令接收月份和年份。如果运行程序没有指定月份和年份，那么，年份就是当前年份，月份就是当前月份。
## MyCalendar类 ##

import java.awt.*;
import java.util.*;


public class MyCalendar extends GregorianCalendar
{
    public int daysInMonth()
    {
        switch(get(MONTH))
        {
        case 0:
        case 2:
        case 4:
        case 6:
        case 7:
        case 9:
        case 11:
            return 31;
        case 1:
            if(isLeapYear(get(YEAR)))
                return 29;
        case 3:
        case 5:
        case 8:
        case 10:
            return 31;
            default : return 0;
        }
    }

    public String getMonthName()
    {
        String monthName=null;


        switch(get(MONTH))
        {
         case 0: monthName = "January"; break;
          case 1: monthName = "Feburary";   break;
          case 2: monthName = "March"; break;
          case 3: monthName = "April"; break;
          case 4: monthName = "May"; break;
          case 5: monthName = "June"; break;
          case 6: monthName = "July"; break;
          case 7: monthName = "August"; break;
          case 8: monthName = "September"; break;
          case 9: monthName = "October"; break;
          case 10: monthName = "November"; break;
          case 11: monthName = "December"; break;
          default:
        }
        return  monthName;
    }

}

## 主函数类 ##

import java.util.*;
public class  display
{
static MyCalendar calendar=new MyCalendar();
public static void main(String[] args)
{
    int month=calendar.get(MyCalendar.MONTH)+1;
    int  year=calendar.get(MyCalendar.YEAR);

    if(args.length>2)
        System.out.println(args[1]);
    else
        if(args.length==2)
        {
            year=Integer.parseInt(args[1]);
            month=Integer.parseInt(args[0]);

            calendar.set(Calendar.YEAR,year);
            calendar.set(Calendar.MONTH,month-1);
        }
        else
            if(args.length==1)
            {
                month=Integer.parseInt(args[0]);

                calendar.set(Calendar.MONTH,month-1);
            }
    calendar.set(Calendar.DATE,1);


    printMonth(year,month);
}


static void printMonth(int year,int month)
{
    int startDay=getStartDay();


    int numOfDaysInMonth=calendar.daysInMonth();


    printMonthTitle(year,month);
    printMonthBody(startDay,numOfDaysInMonth);

    }
static int getStartDay()
{
    return calendar.get(Calendar.DAY_OF_WEEK);
}

static void printMonthTitle(int year,int month)
{
    System.out.println("         "+calendar.getMonthName()+", "+year);
    System.out.println("-----------------------------");
    System.out.println(" Sun Mon Tue Wed Thu Fri Sat");
}



static void printMonthBody(int startDay,int numOfDaysInMonth)
{
    int i = 0;

    for (i = 0; i < startDay-1; i++)
      System.out.print("    ");

    for (i = 1; i <= numOfDaysInMonth; i++) {
      if (i < 10)
        System.out.print("   "+i);
      else
        System.out.print("  "+i);

      if ((i + startDay - 1) % 7 == 0)
        System.out.println();
    }

    System.out.println("");
}
}

## 程序运行结果（未指定年份和月份） ##

## 程序运行结果（指定年份和月份） ##