这里有个万年历的程序 为什么运行之后没有结果 望各位大侠不吝赐教
 import java.applet.*;
 import java.awt.*;
 import java.util.*;
 class calendar extends Applet
 {
     
    
    Graphics g;
     Font font;
     FontMetrics fm;
     Date current_date;
     Date month_to_show;
     int width;
     int height;
     int year;
     int month;
     
    
    public void init()
   {
       g=getGraphics();
       current_date=new Date();
       year=current_date.getYear();
       month=current_date.getMonth();
       month_to_show=new Date(year,month,1);
       Panel p=new Panel();
       add("North",p);
       p.add(new Button("<"));
       p.add(new Button(">"));
       
   }
       public boolean action(Event evt,Object arg)
       {
           if(arg.equals("<"))
           {
               if(--month<0)
               {
                   month=11;
                   year--;
               }
           }
           else
           {
               if(++month>11)
               {
                   month=1;
                   year++;
               }
           }
           month_to_show=new Date(year,month,1);
           repaint();
           return true;
       }
       String day_of_week(int day)
       {
           switch(day)
           {
               case 0:return("Sun");
               case 1:return("Mon");
               case 2:return("Tue");
               case 3:return("Wed");
               case 4:return("Thu");
               case 5:return("Fri");
               default:return("Sun");
           }
       }
       String month_name(int month)
       {
           switch(month)
           {
               case 0:return("January");
               case 1:return("February");
               case 2:return("March");
               case 3:return("April");
               case 4:return("May");
               case 5:return("June");
               case 6:return("July");
               case 7:return("August");
               case 8:return("September");
               case 9:return("October");
               case 10:return("November");
               default:return("December");
           }
       }
       int number_of_days(int month,int year)
       {
           switch(month+1)
           {
               case 1:
               case 3:
               case 5:
               case 7:
               case 8:
               case 10:
               case 12:
               return(31);
               
               case 4:
               case 6:
               case 9:
               case 11:
               return(30);
               
               default:
               if(year%4!=0)
               return(28);
               else 
              if(year%100!=0)
               return(29);
               else
               if(year%400!=0)
               return(28);
               else
               return(29);
           }
       }
       public void paint(Graphics g)
       {
           width=size().width;
           height=size().height;
           
          if(width<height)
           height=width;
           else
           width=height;
           
          g.setColor(Color.blue);
           g.fillRect(0,0,size().width,size().height);
           g.setColor(Color.white);
           
          for(int i=2;i<9;i++)
           {
               int y=(height*i)/8;
               g.drawLine(0,y,width-1,y);
           }
           int y=height/4;
           for(int i=0;i<8;i++)
           {
               int x=(width*i)/7;
               g.drawLine(x,y,x,height-1);
           }
           
          font=new Font("TimesRoman",Font.BOLD,height/20);
           g.setFont(font);
          //font_metrics=g.getFontMetrics();
         
           
          g.drawString(month_name(month_to_show.getMonth())+""+(1900+month_to_show.getYear()),0,height/8);
           y=height/4;
           for(int i=0;i<7;i++)
           {
               g.drawString(day_of_week(i),(width*i)/7,y);
           }
           int first=month_to_show.getDay();
           int last=number_of_days(month_to_show.getMonth(),month_to_show.getYear());
           int day=first;
           y=(height*5)/16;
           for(int i=1;i<=last;i++)
           {
               g.drawString(""+i,(width*day)/7,y);
               if(++day>6)
               {
                   day=0;
                   y+=height/8;
               }
           }
       }
   
 

    public static void main(String args[])
     {
         calendar c=new calendar();
     }
 }