java - 如何计算我的类(class)中的年份差异？

Question

我正在编写一个程序，用户可以在其中输入日期并将其打印出来。此外，该程序还有一个给定的日期来计算与第二个条目的年份差异。我当前的问题是，当我调用计算方法时，一切似乎都正常，但不幸的是输出始终为 0。

这是我的代码:

import java.util.Scanner;
public class Dates{
    static Scanner scan = new Scanner(System.in);
    // Attributes
    static int Day;
    static int Month;
    static int Year;

    //Constructor
    Dates(int x, int y, int z){
        Day = 12;
        Month = 12;
        Year = 2019;
        if(Day > 31) {
            do {
                System.out.println("Wrong day! repeat entry: ");
                Day = scan.nextInt();
            }while (Day > 31);
        }
        if(Month > 12) {
            do {
                System.out.println("Wrong month! repeat entry: ");
                Month = scan.nextInt();
            }while(Month > 12); 
        }
        if(Year < 1800) {
            do {
                System.out.println("Incorrect Year! repeat entry: ");
                Year = scan.nextInt();
            }while(Year < 1800);
        }
    }
//Calculates Year difference
public static int getYeardiff(int day, int month, int year) {
    System.out.println("Press <0>, if you want to know passed years between two dates. ");
    int difference = 0;
    int key = scan.nextInt();
    if(key == 0) {
        System.out.println("Enter a second date: ");
        Dates diffr = new Dates(Day, Month, Year);
        diffr.Day = scan.nextInt();
        diffr.Month = scan.nextInt();
        diffr.Year = scan. nextInt();
        if(diffr.Year <= Dates.Year) {
            difference = Dates.Year - diffr.Year;
            System.out.println(difference);
        }
    }
    return difference;
}
//Formats the date into a String.
public static String asString(int day, int month, int year) {
    String stringDay = "" + Day;
    String stringMonth = "" + Month;
    String stringYear = "" + Year;
    String stringDate = stringDay + "." + stringMonth+ "." + stringYear;
    System.out.println(stringDate);
    return stringDate;
}


public static void main(String[] args) {
    System.out.println("Enter todays date!");
    Dates xmas = new Dates(Day, Month ,Year);
    xmas.Day = scan.nextInt();
    xmas.Month = scan.nextInt();
    xmas.Year = scan.nextInt();
    asString(xmas.Day, xmas.Month, xmas.Year);
    getYeardiff(Day, Month, Year);
    }
}

这是获得更好概览的方法。

public static int getYeardiff(int day, int month, int year) {
   System.out.println("Press <0>, if you want to know passed years between two dates. ");
   int difference = 0;
   int key = scan.nextInt();
   if(key == 0) {
       System.out.println("Enter a second date: ");
       Dates diffr = new Dates(Day, Month, Year);
       diffr.Day = scan.nextInt();
       diffr.Month = scan.nextInt();
       diffr.Year = scan. nextInt();
       if(diffr.Year <= Dates.Year) {
           difference = Dates.Year - diffr.Year;
           System.out.println(difference);
       }
   }
   return difference;
}

如上所述，我得到的输出始终为 0。这是完整的输出:

Enter todays date!
12
12
2019
12.12.2019
Press <0>, if you want to know passed years between two dates. 
0
Enter a second date: 
12
12
1990
0

我的问题是，我必须更改什么才能从我的计算方法中获得正确的输出？

Answer 1

使用大写字母的字段违反了 java 标准。此外，您的 Dates 类的构造函数不会对传入的参数执行任何操作。相反，它们是从扫描仪分配的。这也是违反惯例的。扫描仪应该在外部请求输入，然后您根据用户输入的内容构建类。

我修改了您的代码如下:

首先，您的 Dates 类可以简化为:

int day;
int month;
int year;

//Constructor
Dates(int day, int month, int year) {
  this.day = day;
  this.month = month;
  this.year = year;
}

然后我创建了一个方法来要求输入日期

public static Dates getDates() {
  int day = 0, month = 0, year = 0;

  System.out.print("Enter the day: ");
  day = scan.nextInt();

  while (day > 31 || day < 1) {
    System.out.println("Wrong day! repeat entry: ");
    day = scan.nextInt();
  }

  System.out.print("Enter the month: ");
  month = scan.nextInt();

  while(month > 12 || month < 1) {
    System.out.println("Wrong month! repeat entry: ");
    month = scan.nextInt();
  }

  System.out.print("Enter the year: ");
  year = scan.nextInt();
  while(year > 9999 || year < 1800 ) {
    System.out.println("Incorrect Year! repeat entry: ");
    year = scan.nextInt();
  }

  return new Dates(day, month, year);
}

这会简化您的 getYeardiff 和 asString 函数:

//Calculates Year difference
public static int getYeardiff(Dates other) {
  Scanner scanner = new Scanner(System.in);
  System.out.print("Press <0>, if you want to know passed years between two dates. ");
  int difference = 0;
  int key = scan.nextInt();
  if(key == 0) {
    System.out.println("Enter a second date: ");

    Dates diffr = getDates();

    difference = Math.abs(diffr.year - other.year);
    System.out.println(difference);
  }
  return difference;
}

//Formats the date into a String.
public static String asString(Dates other) {
  String stringDay = "" + other.day;
  String stringMonth = "" +other.month;
  String stringYear = "" + other.year;
  String stringDate = stringDay + "." + stringMonth+ "." + stringYear;
  System.out.println(stringDate);
  return stringDate;
}

最后是你的main方法:

public static void main(String[] args) {
  System.out.println("Enter todays date!");
  Dates xmas = getDates();
  asString(xmas);
  getYeardiff(xmas);
  scan.close();
}