individual/src/Login.java

import java.io.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Login {
	private static final String USER_FILE = "users.txt";
    private static List<User> users = new ArrayList<>();
    public void Main() {    	
    	load();
        Scanner scanner = new Scanner(System.in);        
        while (true) {
            System.out.println("\n---------登录系统---------");
            System.out.println("请输入用户名和密码（用空格隔开）: ");
            String input = scanner.nextLine().trim(); 
            if (input.equalsIgnoreCase("q")) {
                System.out.println("\n已退出！");
                break;
            } 
            String[] NandP = input.split(" "); 
            if (NandP.length != 2) {
                System.out.println("请输入正确的用户名和密码！");
                continue;
            }
            String username = NandP[0];
            String password = NandP[1];
            User user = Prove(username, password);
            if (user != null) {
                Success(user, scanner);
            } else {
                System.out.println("请输入正确的用户名和密码！");
            }
        }
        scanner.close();
    }
      
    private static void load() {
        users.clear();
        try (BufferedReader reader = new BufferedReader(new FileReader(USER_FILE))) {
            String line;
            while ((line = reader.readLine()) != null) {
                line = line.trim();
                if (!line.isEmpty()) {
                    String[] parts = line.split(" ");
                    if (parts.length == 3) {
                        users.add(new User(parts[0], parts[1], parts[2]));
                    }
                }
            }
            reader.close();
            System.out.println("Loading...");
        } catch (IOException e) {
            System.out.println("出错！" + e.getMessage());
        }
    }
    
    private static User Prove(String username, String password) {
        for (User user : users) {
            if (user.getUsername().equals(username) && user.getPassword().equals(password)) {
                return user;
            }
        }
        return null;
    }
    
    private static void Success(User user, Scanner scanner) {
    	String role = getRole(user.getRole());
        System.out.println("\n登录成功！\n" + user.getUsername() + " [" + role + "]");
        QuestionManager questionManager = new QuestionManager(user.getUsername(), user.getRole());
        while (true) {
            System.out.println("\n输入 -1 退出登录，输入 q 退出程序，输入\"切换为XX\"切换难度（XX为小学、初中、高中）");
            System.out.println("准备生成[" + questionManager.getCurrentRoleChinese() + "]数学题目，请输入生成题目数量（10~30）：");
            String input = scanner.nextLine().trim();
            if (input.equals("-1")) {
                System.out.println("返回登录界面...");
                break;
            } else if (input.equalsIgnoreCase("q")) {
                System.out.println("\n已退出！");
                System.exit(0);
            } else if (input.startsWith("切换为")) {
                Switch(questionManager, input);
            } else {
                try {
                    int count = Integer.parseInt(input);
                    if (count >= 10 && count <= 30) {
                        questionManager.generateQuestions(count);
                    } else if (count == -1) {
                        System.out.println("返回登录界面...");
                        break;
                    } else {
                        System.out.println("题目数量应在10~30之间!");
                    }
                } catch (NumberFormatException e) {
                    System.out.println("请输入有效的数字（10~30）或指定命令!");
                }
            }
        }
    }
    
    private static void Switch(QuestionManager questionManager, String input) {
    	String newRole = input.substring(3).trim();
        switch (newRole) {
            case "小学":
                questionManager.setRole("primary");
                System.out.println("已切换为小学难度");
                break;
            case "初中":
                questionManager.setRole("junior");
                System.out.println("已切换为初中难度");
                break;
            case "高中":
                questionManager.setRole("senior");
                System.out.println("已切换为高中难度");
                break;
            default:
                System.out.println("请输入小学、初中和高中三个选项中的一个");
        }
    }
    
    private static String getRole(String role) {
        switch (role) {
            case "primary":
                return "小学";
            case "junior":
                return "初中";
            case "senior":
                return "高中";
            default:
                return "未知";
        }
    }
    
}