万年历结果问题

package xiti;
import java.util.Scanner;

public class caleldar {

    public static void main(String[] args) {
        int sum=0;
        Scanner s=new Scanner(System.in);
        System.out.println("请输入年份");
        int year=s.nextInt();
        System.out.println("请输入月份");
        int month=s.nextInt();

        for(int i=1900;i<year;i++){
            if(i%4==0&&i%100!=0||i%400==0){
                sum+=366;
            }else{
                sum+=365;
            }
        }
        
        for(int i=1;i<month;i++){
            if(i==2){
                if(year%4==0&&year%100!=0||year%400==0){
                    sum+=29;
                }else{sum+=28;}
            }else if(i==4||i==6||i==9||i==11){
                sum+=30;
            }else{sum+=31;}
            
            }sum+=1;
        System.out.println("日\t一\t二\t三\t四\t五\t六");
        for(int i=1;i<sum%7;i++){
            System.out.print("\t");
        }   
        
            for(int i=1;i<=30;i++){
            if(sum%7==6){System.out.print(i+"\n");}
            else {System.out.print(i+"\t");}
            sum++;
        }    if(month==1||month==3||month==5||month==7||month==8||month==10||month==12){
            System.out.print("31");
        }

    }

}
输入2012年 1月 还是对的 但是你看看2016年 8月 就不对了。。求解答