方法总结

import java.time.LocalDate;
import java.time.temporal.ChronoUnit;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int year = scanner.nextInt();
        int month = scanner.nextInt();
        int day = scanner.nextInt();
        LocalDate date = LocalDate.of(year, month, day);
        LocalDate date01 = LocalDate.of(year, 1, 1);
        long days = date01.until(date, ChronoUnit.DAYS);
        System.out.println(days+1);
    }
}

普通方法

import java.util.*;
public class Main{
    public static final int[] mon={
        0,31,28,31,30,31,30,31,30,31,30,31,30
    };
    public static void main(String[] args) {
        //如果是闰年， 2月是 29天， 否则 是 2天
        Scanner sc = new Scanner(System.in);
        int year = sc.nextInt();
        int month = sc.nextInt();
        int day = sc.nextInt();
        if( year%400==0||(year%100!=0&&year%4==0) ) {
            mon[2] = 29;

        }
        int res = 0;


        for(int i=1;i<month;++i) {
            res+=mon[i];
        }
        res+=day;
        System.out.println(res);
    }








}