Java使用Scanner扫描文件时else if分支无法正常执行问题求助

核心问题定位 #

你的代码跑不通主要是3个逻辑漏洞：

• 输入判断循环中else if(no)分支的break被你注释了，导致用户输入no之后不会跳出循环，会先打印「无效输入」再重新要求输入姓氏，永远走不到后面的文件读取逻辑
• 无论用户选yes还是no，代码都强制执行了discount = scan.nextDouble()要求输入折扣值，和你要的「选no就不用自定义折扣」的逻辑完全不符
• Scanner的nextDouble()方法不会吃掉输入后的换行符，如果后面用nextLine()会直接读到空字符串，触发逻辑异常

修复思路 #

1. 先在分支外层初始化折扣的默认值：选no的话直接用0折扣（不减免），选yes的话再接收用户输入修改折扣值，解决变量跨分支访问的问题
2. 补全else if(no)分支的break，保证合法输入后直接跳出输入循环
3. 把折扣输入的逻辑移到yes分支内部，选no的时候跳过这一步
4. 所有文件读取逻辑统一放在输入判断循环之后，不需要重复写在分支内，因为此时discount已经有确定的有效值
5. 调用nextDouble()后手动加一行scan.nextLine()吃掉残留的换行符，避免后续输入异常

修复后完整代码 #

import java.io.FileReader;
import java.util.Scanner;
import java.io.FileNotFoundException;

public class Coursework2 {
    
    public static void main(String[] args)
    throws FileNotFoundException {
        Scanner reader = new Scanner(new FileReader("seats.txt"));
        Scanner scan = new Scanner (System.in);
        // 初始化默认折扣为0，即选no时无折扣
        double discount = 0;
        boolean loopFlag = true;

        // 输入校验循环
        while (loopFlag) {
            System.out.println("Please enter your Surname:");
            String name = scan.nextLine();
            System.out.println("Good morning, Manager "  + name + " Would you like to apply a specific discount rate?");
            String decision = scan.nextLine();

            if (decision.equalsIgnoreCase("yes") || decision.equalsIgnoreCase("y")) {
                System.out.println("That's great, Mananger " + name + ".");
                System.out.println("How much discount would you like? (1-100)");
                discount = scan.nextDouble();
                // 吃掉nextDouble残留的换行符
                scan.nextLine();
                loopFlag = false;
            } else if (decision.equalsIgnoreCase("no") || decision.equalsIgnoreCase("n")) {
                System.out.println("Alright, " + name + " Here's all the seats without discounts:");
                loopFlag = false;
            } else {
                System.out.println("Invalid Input, please try again. Restarting.");
            }
        }
        
        // 统一执行文件读取逻辑
        while (reader.hasNext()) {
            String table = reader.next();
            double price = reader.nextDouble();
            int bookings = reader.nextInt();
            
            double newdiscount = (((price/100.00*discount)*bookings));
            double newincome = (price*bookings-(((price/100.00*discount)*bookings)));
            System.out.printf("Seat type: %s, Price: £%.2f, Bookings: %d %n",table, price, bookings );
            System.out.printf("Discount: £%.2f, Income: £%.2f %n", newdiscount, newincome);
            
            String decision;
            do {
                System.out.printf("Seat type: %s, Price: £%.2f, Bookings: %d %n",table, price, bookings );
                decision = scan.next();
            } while (decision.equalsIgnoreCase("No"));
            System.out.printf("Seat type: %s, Price: £%.2f, Bookings: %d %n",table, price, bookings );
        }
        
        reader.close();
        scan.close();
    }
}

内容的提问来源于stack exchange，提问作者MrKalius