万年历的编写（java）

import java.util.Scanner;
public class CalendarDemo{
    public static void main(String []args){
        int year;
        int month;
        int days=0;
        int sumdays=0;
        boolean isRn;
        System.out.println("************万年历查询*************");
        Scanner input=new Scanner(System.in);
        System.out.println("请输入年份：");
        year=input.nextInt();
        System.out.println("请输入月份");
        month=input.nextInt();
        if((year%400==0)||(year%4==0&&year%100!=0)){
            isRn=true;
            System.out.println(year+"是润年");
        }
        else{
            isRn=false;
            System.out.println(year+"不是润年");
        }
        //计算总的天数
        for(int i=1900;i<year;++i){
            if(i%400==0||(i%4==0&&i%100!=0)){
                sumdays+=366;
            }
            else{
                sumdays+=365;
            }
        }
        for(int j=1;j<=month;j++){
            switch(j){
                case 1:
                case 3:
                case 5:
                case 7:
                case 8:
                case 10:
                case 12:
                days=31;
                break;
                case 2:
                if(isRn){
                    days=29;
                    }else{
                        days=28;
                    }
                    break;
                    case 4:
                    case 6:
                    case 9:
                    case 11:
                    days=30;
                    break;
            }
            if(month!=j){
                sumdays+=days;
            }
        }
        //求出星期几
        int beforedays;
        beforedays=1+sumdays%7;
        //星期天第一列前面不需要制表符；
        if(beforedays==7){
            beforedays=0;
        }
        System.out.println("星期天\t星期一\t星期二\t星期三\t星期四\t星期五\t星期六");
        for(int i=0;i<beforedays;++i){
            System.out.print("\t");
        }
        for(int j=1;j<=days;++j){
            System.out.print(j+"\t");
            if((j+beforedays)%7==0){
                System.out.println();
            }
        }
    }
}