一个用java代码编写的日期程序

import java.util.*;

public class student
{
    public static void main(String[] args)
    {
        GregorianCalendar d=new GregorianCalendar();
        int today=d.get(Calendar.DAY_OF_MONTH);
        int month=d.get(Calendar.MONTH);
        d.set(Calendar.DAY_OF_MONTH,1);
        int weekday=d.get(Calendar.DAY_OF_WEEK);
      
       
        System.out.println("sun mon tue wed thu fri sat");
        for(int i=Calendar.SUNDAY;i<weekday;i++)
        System.out.print("");
        do
        {
            int day=d.get(Calendar.DAY_OF_MONTH);
        if (day == 1&&weekday!=7)
        {
            for(int x =0;x<4*(weekday-1);x++) {
                System.out.print(" ");
            }
        }
                               
            if(day<10 )  System.out.print(" ");
                           System.out.print(day);
            if(day==today)
            System.out.print("* ");
            else
            System.out.print("  ");
            if(weekday==Calendar.SATURDAY )
            System.out.println();
           
            d.add(Calendar.DAY_OF_MONTH,1);
            weekday=d.get(Calendar.DAY_OF_WEEK);
        }
        while(d.get(Calendar.MONTH)==month);
       
    }
}