Java 程序，当给定一个数字时返回一个日期，并在给定另一个数字时返回将来的日期

好的，所以我正在尝试创建一个程序，当给定一个从 0 到 6 的数字时，它将返回一周中的某一天(例如 0 = 星期日，1 = 星期一......之后，它将要求用户输入另一个数字，并计算出该天数中的哪一天。所以它看起来像这样：

输入数字：0
输入已过去的天数：4
现在是星期天，将来是星期四

我尝试了几种不同的方法，但似乎找不到一种有效的方法。这是我提出的最新内容：

import java.util.Scanner;
public class code
{
    public static void main (String[] args)
    {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter today's day:");
        int num = scanner.nextInt();
        
        if(num > 6 || num < 0) {
            System.out.println("This is an invalid number");
        }
        
        switch(num) {
            case 0:
                String day = "Sunday";
                break;
            case 1:
                String day = "Monday";
                break;
            case 2:
                String day = "Tuesday";
                break;
            case 3:
                String day = "Wednesday";
                break;
            case 4:
                String day = "Thursday";
                break;
            case 5:
                String day = "Friday";
                break;
            case 6:
                String day = "Saturday";
                break;
        }
        
        Scanner scanner2 = new Scanner(System.in);
        System.out.println("Enter the number of days elapsed since today:");
        int num2 = scanner2.nextInt();
        
        
        
        int newday = num + num2;
        
        while(newday > 6) {
            newday = newday - 7;
        }
        
        switch(newday) {
            case 0:
                String day2 = "Sunday";
                break;
            case 1:
                String day2 = "Monday";
                break;
            case 2:
                String day2 = "Tuesday";
                break;
            case 3:
                String day2 = "Wednesday";
                break;
            case 4:
                String day2 = "Thursday";
                break;
            case 5:
                String day2 = "Friday";
                break;
            case 6:
                String day2 = "Saturday";
                break;
        }
            
        
        System.out.println("Today is " + day + " and the future day is " + day2);
    }
}

以下是编译器给我的错误：

14 errors found:
File: C:Usersexercise_4_5.java  [line: 19]
Error: variable day is already defined in method main(java.lang.String[])
File: C:Userscode.java  [line: 22]
Error: variable day is already defined in method main(java.lang.String[])
File: C:Userscode.java  [line: 25]
Error: variable day is already defined in method main(java.lang.String[])
File: C:Userscode.java  [line: 28]
Error: variable day is already defined in method main(java.lang.String[])
File: C:Userscpde.java  [line: 31]
Error: variable day is already defined in method main(java.lang.String[])
File: C:Userscode.java  [line: 34]
Error: variable day is already defined in method main(java.lang.String[])
File: C:Userscode.java  [line: 55]
Error: variable day2 is already defined in method main(java.lang.String[])
File: C:Userscode.java  [line: 58]
Error: variable day2 is already defined in method main(java.lang.String[])
File: C:Userscode.java  [line: 61]
Error: variable day2 is already defined in method main(java.lang.String[])
File: C:Userscode.java  [line: 64]
Error: variable day2 is already defined in method main(java.lang.String[])
File: C:Userscode.java  [line: 67]
Error: variable day2 is already defined in method main(java.lang.String[])
File: C:Userscode.java  [line: 70]
Error: variable day2 is already defined in method main(java.lang.String[])
File: C:Userscode.java  [line: 75]
Error: cannot find symbol
  symbol:   variable day
  location: class code
File: C:UsersDesktopcode.java  [line: 75]
Error: cannot find symbol
  symbol:   variable day2
  location: class code

我对编程很陌生，Java是我的第一语言。任何帮助和修复将不胜感激。提前谢谢你。

import java.util.Scanner;

/**
 *
 * @author wathsara
 */
public class Code {

    public static void main (String[] args)
    {
        String day="",day2="";
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter today's day:");
        int num = scanner.nextInt();
        if(num > 6 && num < 0) {
            System.out.println("This is an invalid number");
        }
        switch(num) {
            case 0:
                day = "Sunday";
                break;
            case 1:
                day = "Monday";
                break;
            case 2:
                day = "Tuesday";
                break;
            case 3:
                day = "Wednesday";
                break;
            case 4:
                day = "Thursday";
                break;
            case 5:
                day = "Friday";
                break;
            case 6:
                day = "Saturday";
                break;
        }
        Scanner scanner2 = new Scanner(System.in);
        System.out.println("Enter the number of days elapsed since today:");
        int num2 = scanner2.nextInt();

        int newday = num + num2;
        while(newday > 6) {
            newday = newday - 7;
        }
        switch(newday) {
            case 0:
                day2 = "Sunday";
                break;
            case 1:
                day2 = "Monday";
                break;
            case 2:
                day2 = "Tuesday";
                break;
            case 3:
                day2 = "Wednesday";
                break;
            case 4:
                day2 = "Thursday";
                break;
            case 5:
                day2 = "Friday";
                break;
            case 6:
                day2 = "Saturday";
                break;
        }

        System.out.println("Today is " + day + " and the future day is " + day2);
    }
}

试试上面的代码。问题是你声明了一个字符串变量 day 6 次，字符串变量 day2 6 次，这就是代码没有执行的原因。

在我看来，您的解决方案不是很有效。这是关于算法，而不是Java语言本身。试试这个：

一次接收 2 个输入。
初始化从星期日 (索引：0( 到星期六 (索引： 6( 的数组或列表
将这两个输入相加，并在将其除以 7 时取余数。我希望余数的结果是从 0 到 6
获取数组在余数索引处

没

关系，这是一个简单的修复。我在开关案例语句外部而不是内部声明了变量"day"和"day2"。

import java.util.Scanner;
public class exercise_4_5
{
    public static void main (String[] args)
    {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter today's day:");
        int num = scanner.nextInt();
        
        if(num > 6 || num < 0) {
            System.out.println("This is an invalid number");
        }
        
        String day = "Invalid";
        
        switch(num) {
            case 0:
                day = "Sunday";
                break;
            case 1:
                day = "Monday";
                break;
            case 2:
                day = "Tuesday";
                break;
            case 3:
                day = "Wednesday";
                break;
            case 4:
                day = "Thursday";
                break;
            case 5:
                day = "Friday";
                break;
            case 6:
                day = "Saturday";
                break;
        }
        
        Scanner scanner2 = new Scanner(System.in);
        System.out.println("Enter the number of days elapsed since today:");
        int num2 = scanner2.nextInt();
        
        
        
        int newday = num + num2;
        
        while(newday > 6) {
            newday = newday - 7;
        }
        
        String day2 = "Invalid";
        
        switch(newday) {
            case 0:
                day2 = "Sunday";
                break;
            case 1:
                day2 = "Monday";
                break;
            case 2:
                day2 = "Tuesday";
                break;
            case 3:
                day2 = "Wednesday";
                break;
            case 4:
                day2 = "Thursday";
                break;
            case 5:
                day2 = "Friday";
                break;
            case 6:
                day2 = "Saturday";
                break;
        }
            
        
        System.out.println("Today is " + day + " and the future day is " + day2);
    }
}

在开关外的每个开关案例中声明这些字符串变量，并在第 1 天和第 2 天创建，它将起作用。

有很多事情会使你的代码效率非常低下。以下是一些改进

所有重复的代码都应该在一个函数中。获取数字并获取日期的代码应该是不同的函数(切换大小写(。
使用 % (Mod( 运算符获取 newDay 的日期，而不是 while 循环。 newDay = (num1 + num2)%7
您可以使用地图代替开关盒。

String day和String day2的范围仅限于开关外壳内部，不能在开关外壳外使用。在外部声明变量，只需更改 switch 语句中的值。

import java.util.HashMap;
import java.util.Scanner;
import java.util.Map;
class Ideone {

    private static String getDay(int num){
        Map<Integer, String> days = new HashMap<Integer, String>();
        days.put(0, "Sunday");
        days.put(1, "Monday");
        days.put(2, "Tuesday");
        days.put(3, "Wednesday");
        days.put(4, "Thursday");
        days.put(5, "Friday");
        days.put(6, "Saturday");
        return days.get(num);
    }
    public static void main(String[] args){
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter today's day: ");
        int num = scanner.nextInt();
        System.out.println("Enter the number of days elapsed since today: ");
        int num2 = scanner.nextInt();
        if (num < 0 || num > 6){
            System.out.println("Invalid Number");
            System.exit(0);
        }
        int newDay = (num + num2) % 7;
        System.out.println("Today is " + getDay(num) + " and the future day is " + getDay(newDay));
    }
}

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