import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeFormatterBuilder;
import java.time.temporal.ChronoUnit;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNext()) {
            LocalDate date1 = LocalDate.parse(scanner.next(),
                                 DateTimeFormatter.BASIC_ISO_DATE);
            LocalDate date2 = LocalDate.parse(scanner.next(),
                                 DateTimeFormatter.BASIC_ISO_DATE);
            System.out.println(date1.until(date2, ChronoUnit.DAYS) + 1);
        }
    }
}

官方文档:[https://www.runoob.com/manual/jdk11api/java.base/java/time/LocalDate.html]

LocalDate.parse(string,formatter)将字符串按照指定模式格式化为LocalDate对象。