编写一个类,根据年月日,能算出这一天是星期几?怎么写这个程序,在线等

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class YMD {

private static final SimpleDateFormat adf = new SimpleDateFormat("yyyy-MM-dd",java.util.Locale.CHINA);
private static final Calendar calendar = Calendar.getInstance(java.util.Locale.CHINA);
private static final String[] weekdays = {"星期日","星期一","星期二","星期三","星期四","星期五","星期六",};

public static String weekday(int y,int m,int d) throws Exception{
return weekday(""+y,""+m,""+d);
}

public static String weekday(String y,String m,String d) throws Exception{
return weekday(y+"-"+m+"-"+d);
}

//2008-1-1
public static String weekday(String ymd) throws Exception{
Date date = adf.parse(ymd);
calendar.setTime(date);
int weekday = cale