java实现任意年份的日历打印

初学，示例代码里看到的觉得很强大，自己也试试。

package du;

import java.util.Scanner;
public class Test {
    public static void main(String argv[]){
        while(true){
        System.out.println("输入年份:");
        Scanner sc=new Scanner(System.in);
        int year=sc.nextInt();
        System.out.println(year);
        System.out.println();
        for(int i=1;i<13;i++){
            System.out.println(i+"月");
            System.out.println("----------------------------------");
            System.out.println("星期日    星期一    星期二   星期三   星期四    星期五    星期六");
            ShowMonth(year,i);
        }
        }
    }
    public static void ShowMonth(int year,int month){
        int firstday=weekday(year, month, 1);
        for(int i=0;i<firstday;i++){
            System.out.print("     ");
        }
        for(int j=1;j<=daysofMonth(year, month);j++){
            if(j<10){
            System.out.print("0"+j+"   ");
            }
            else
                System.out.print(j+"   ");
            
            if(firstday==6){
                System.out.println();
                firstday=-1;
            }
            firstday++;
        }
        System.out.println();
        System.out.println("----------------------------------");
    }
    public static boolean isLeapYear(int year){
        boolean flag = false;

        if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0)
            flag = true;
        else
            flag = false;
        return flag;
    }
    
    public static int weekday(int year,int month,int day){
        long amount=0;
        for(int i=1;i<year;i++){
            if(isLeapYear(i))
                amount++;
        }
        amount+=365*(year-1);
        for(int i=1;i<month;i++){
            amount+=daysofMonth(year, i);
        }
        amount+=day;
        //System.out.println(amount);
        int week=(int) (amount%7);
        return week;    
    }
    private static int daysofMonth(int year,int month){
        
        switch(month){
        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;
        case 2: if(isLeapYear(year))
            return 29;
        else
            return 28;
        default :return 0;
        }
        
    }
    
}