如何将星期字符串映射为整数并实现Java星期增减功能？

你现在的代码用了大量if语句处理星期的映射和加减，既冗余又不易维护，下面是针对需求的优化方案，重点解决添加天数的分支问题，同时优化整体代码结构。

现有代码 #

import java.util.Scanner;
public class Main
{
public static void main(String[] args)
{
        Day.userInput();
    }
}

class Day
{
static int b;
public static void userInput()
{
Scanner scan = new Scanner(System.in);

// set day of week
System.out.println("Please set the day of the week:");
String day = scan.nextLine();

        if(day.equals("sunday") || (day.equals("Sunday")) )
        {
          b = 1;
        }
        if(day.equals("monday") || (day.equals("Monday")) )
        {
            b = 2;
        }
        if(day.equals("tuesday") || (day.equals("Tuesday")) )
        {
            b = 3;
        }
        if(day.equals("wednesday") || (day.equals("Wednesday")) )
        {
            b = 4;
        }
        if(day.equals("thursday") || (day.equals("Thursday")) )
        {
            b = 5;
        }
        if(day.equals("friday") || (day.equals("Friday")) )
        {
            b = 6;
        }
        if(day.equals("saturday") || (day.equals("Saturday")) )
        {
            b = 7;
        }
    
    
        System.out.println("Enter 1 to return the day.\nEnter 2 to return tomorrows day.\nEnter 3 to return yesterdays day.\nEnter 4 to add days to the current day.\n");
        int a = scan.nextInt();

// return day
if(a == 1)
{
System.out.println("The day is " + day);
}
//return next day
if(a == 2)
{
if ( b == 1)
{
System.out.println("The next day is Monday.");
}
if (b == 2)
{
System.out.println("The next day is Tuesday.");
}
if (b == 3)
{
System.out.println("The next day is Wednesday.");
}
if (b == 4)
{
System.out.println("The next day is Thursday.");
}
if (b == 5)
{
System.out.println("The next day is Friday.");
}
if (b == 6)
{
System.out.println("The next day is Saturday.");
}
if (b == 7)
{
System.out.println("The next day is Sunday.");
}
        }

//return previous day
if(a == 3)
{
if( b == 1)
{
System.out.println("The previous day was Saturday.");
}
if (b == 2)
{
System.out.println("The previous day was Sunday.");
}
if (b == 3)
{
System.out.println("The previous day was Monday.");
}
if (b == 4)
{
System.out.println("The previous day was Tuesday.");
}
if (b == 5)
{
System.out.println("The previous day was Wednesday.");
}
if (b == 6)
{
System.out.println("The previous day was Thursday.");
}
if (b == 7)
{
System.out.println("The previous day was Friday.");
}
}
// add days  
if(a == 4 )
{
System.out.println("Enter the number of days you want to add");
int c = scan.nextInt();
        }
    }
}

核心优化方案 #

1. 用数组替代if做星期映射 #

把星期字符串和格式化后的星期名分别存进数组，实现字符串与索引的双向转换，彻底消除大量if判断：

// 小写数组用于匹配用户输入，格式化数组用于输出结果
private static final String[] DAYS_LOWER = {"sunday", "monday", "tuesday", "wednesday", "thursday", "friday", "saturday"};
private static final String[] DAYS_FORMATTED = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};

用户输入转小写后，遍历数组就能拿到对应的索引，不用逐个判断大小写。

2. 模运算处理星期循环 #

星期是7天一个周期，利用模运算直接计算加减后的星期索引，无需分支判断：

• 次日：(当前索引 + 1) % 7
• 前日：(当前索引 - 1 + 7) % 7（加7避免索引变为负数）
• 添加n天：(当前索引 + n) % 7，若n为负数，同样加7修正索引确保非负

3. 代码结构优化 #

• 移除静态变量b，改用局部变量存储当前星期索引，避免全局副作用
• 将功能拆分为独立方法（如getDayIndex()负责字符串转索引），代码职责更清晰
• 增加输入合法性校验，处理用户输入无效星期或功能选项的情况，提升程序健壮性

优化后的完整代码 #

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        DayHandler.handleUserInput();
    }
}

class DayHandler {
    // 索引对应：0=周日，1=周一，...，6=周六
    private static final String[] DAYS_LOWER = {"sunday", "monday", "tuesday", "wednesday", "thursday", "friday", "saturday"};
    private static final String[] DAYS_FORMATTED = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};

    public static void handleUserInput() {
        Scanner scan = new Scanner(System.in);

        // 获取并验证用户输入的星期
        int currentIndex = -1;
        while (currentIndex == -1) {
            System.out.println("Please set the day of the week:");
            String inputDay = scan.nextLine().trim().toLowerCase();
            currentIndex = getDayIndex(inputDay);
            if (currentIndex == -1) {
                System.out.println("Invalid day, please enter a valid day (e.g., Monday, sunday).");
            }
        }

        // 功能选择循环
        while (true) {
            System.out.println("\nEnter 1 to return the day.\nEnter 2 to return tomorrow's day.\nEnter 3 to return yesterday's day.\nEnter 4 to add days to the current day.\nEnter 0 to exit.");
            if (!scan.hasNextInt()) {
                System.out.println("Invalid input, please enter a number between 0-4.");
                scan.next(); // 清除无效输入
                continue;
            }
            int choice = scan.nextInt();
            switch (choice) {
                case 0:
                    System.out.println("Exiting program.");
                    scan.close();
                    return;
                case 1:
                    System.out.println("The day is " + DAYS_FORMATTED[currentIndex]);
                    break;
                case 2:
                    int nextIndex = (currentIndex + 1) % 7;
                    System.out.println("The next day is " + DAYS_FORMATTED[nextIndex]);
                    break;
                case 3:
                    int prevIndex = (currentIndex - 1 + 7) % 7;
                    System.out.println("The previous day was " + DAYS_FORMATTED[prevIndex]);
                    break;
                case 4:
                    System.out.println("Enter the number of days you want to add (negative numbers subtract days):");
                    while (!scan.hasNextInt()) {
                        System.out.println("Invalid input, please enter an integer.");
                        scan.next();
                    }
                    int daysToAdd = scan.nextInt();
                    int newIndex = (currentIndex + daysToAdd) % 7;
                    // 处理负数取模的异常情况
                    newIndex = newIndex < 0 ? newIndex + 7 : newIndex;
                    System.out.println("After " + daysToAdd + " days, the day is " + DAYS_FORMATTED[newIndex]);
                    break;
                default:
                    System.out.println("Invalid choice, please enter a number between 0-4.");
            }
        }
    }

    // 根据小写星期字符串获取对应索引
    private static int getDayIndex(String dayLower) {
        for (int i = 0; i < DAYS_LOWER.length; i++) {
            if (DAYS_LOWER[i].equals(dayLower)) {
                return i;
            }
        }
        return -1; // 未找到返回-1表示输入无效
    }
}

关键优化点说明 #

• 数组映射：彻底消除大量if判断，代码更简洁易维护，后续新增或修改星期只需调整数组即可
• 模运算：利用星期的周期性，用数学计算替代分支判断，逻辑清晰且高效
• 输入校验：避免因无效输入导致程序崩溃，提升用户体验
• 结构拆分：代码职责明确，可读性和可维护性大幅提升

内容的提问来源于stack exchange，提问作者Leek