import java.util.Scanner; public class Login { private static String username = "张三"; private static String password = "123456"; public static void main(String[] args) throws ToomanyErrorsException, NamePasswordMismatchException { Scanner scanner = new Scanner(System.in); int count = 0; System.out.println("请输入用户名: "); String username = scanner.next(); while (true) { System.out.println("请输入密码: "); String password = scanner.next(); if ("登录成功".equals(login(username, password))) { System.out.println("登录成功"); break; } count++; if (count==3){ throw new ToomanyErrorsException("密码输入次数已达上限！！！"); } } } public static String login(String username, String password) throws NamePasswordMismatchException { if (!Login.username.equals(username)) { System.out.println("该用户名尚未注册，请核对后输入"); return "用户名有误"; } else { if (!Login.password.equals(password)) { try { throw new NamePasswordMismatchException("密码输入有误"); } catch (Exception e) { e.printStackTrace(); } } else { return "登录成功"; } return "密码有误"; } } }补全两个自定义异常类

以下是两个自定义异常类的补全代码：

1. ToomanyErrorsException

public class ToomanyErrorsException extends Exception {
    public ToomanyErrorsException(String message) {
        super(message);
    }
}

2. NamePasswordMismatchException

public class NamePasswordMismatchException extends Exception {
    public NamePasswordMismatchException(String message) {
        super(message);
    }
}

这两个异常类都继承了Java内置的Exception类，并实现了自己的构造函数。在这个例子中，ToomanyErrorsException用于处理密码输入错误次数过多的情况，而NamePasswordMismatchException则用于处理用户名和密码不匹配的情况。通过这两个自定义异常类，我们可以更好地处理程序中出现的异常情况，使程序更加健壮和稳定。

相关问题

import java.util.Scanner; public class Login { private static String username = "张三"; private static String password = "123456"; public static void main(String[] args) throws ToomanyErrorsException, NamePasswordMismatchException { Scanner scanner = new Scanner(System.in); int count = 0; System.out.println("请输入用户名: "); String username = scanner.next(); while (true) { System.out.println("请输入密码: "); String password = scanner.next(); if ("登录成功".equals(login(username, password))) { System.out.println("登录成功"); break; } count++; if (count==3){ throw new ToomanyErrorsException("密码输入次数已达上限！！！"); } } } public static String login(String username, String password) throws NamePasswordMismatchException { if (!Login.username.equals(username)) { System.out.println("该用户名尚未注册，请核对后输入"); return "用户名有误"; } else { if (!Login.password.equals(password)) { try { throw new NamePasswordMismatchException("密码输入有误"); } catch (Exception e) { e.printStackTrace(); } } else { return "登录成功"; } return "密码有误"; } } }哪里有问题

代码中存在以下问题：

1. 异常处理不恰当。在 `login` 方法中，当密码输入有误时，应该抛出 `NamePasswordMismatchException` 异常。但是，在异常处理代码中，只是简单地打印了堆栈信息，没有处理异常。应该将异常向上抛出，由 `main` 方法中的异常处理代码来处理。

2. 代码中的变量名冲突。在 `main` 方法中，定义了一个名为 `username` 的局部变量，与类中的静态变量 `username` 名称相同，会导致局部变量覆盖类中的静态变量。应该使用不同的变量名，或者使用 `this.username` 来引用类中的静态变量。

3. 没有处理用户名输入有误的情况。当输入的用户名与预设的用户名不一致时，应该提示用户该用户名尚未注册，并要求重新输入用户名。

4. 在 `login` 方法中，当密码输入有误时，返回的字符串为 "密码有误"，但是实际上应该抛出 `NamePasswordMismatchException` 异常。

下面是修改过后的代码：

import java.util.Scanner;

public class Login {
    private static String username = "张三";
    private static String password = "123456";

    public static void main(String[] args) throws ToomanyErrorsException, NamePasswordMismatchException {
        Scanner scanner = new Scanner(System.in);
        int count = 0;
        System.out.println("请输入用户名: ");
        String inputUsername = scanner.next();
        while (!username.equals(inputUsername)) {
            System.out.println("该用户名尚未注册，请核对后输入");
            System.out.println("请输入用户名: ");
            inputUsername = scanner.next();
        }
        while (true) {
            System.out.println("请输入密码: ");
            String inputPassword = scanner.next();
            if ("登录成功".equals(login(inputUsername, inputPassword))) {
                System.out.println("登录成功");
                break;
            }
            count++;
            if (count == 3) {
                throw new ToomanyErrorsException("密码输入次数已达上限！！！");
            }
        }
    }

    public static String login(String username, String password) throws NamePasswordMismatchException {
        if (!Login.password.equals(password)) {
            throw new NamePasswordMismatchException("密码输入有误");
        } else {
            return "登录成功";
        }
    }
}

用Java编写一个《学生信息管理系统》里面有功能1．系统需求分析、初始化信息模块（学生类、用户类）； 2．用户登录界面模块； 3. 学生信息管理主菜单界面模块； 4．学生信息添加模块； 5．学生信息修改模块； 6．学生信息删除模块； 7．学生信息查询模块； 8. 用户信息查询模块； 9. 用户密码修改模块；

好的，以下是一个简单的学生信息管理系统的Java代码：

1. 学生类和用户类

public class Student {
    private String name;
    private String id;
    private String gender;
    private String major;
    private double score;

    // 构造函数
    public Student(String name, String id, String gender, String major, double score) {
        this.name = name;
        this.id = id;
        this.gender = gender;
        this.major = major;
        this.score = score;
    }

    // getter和setter方法
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public String getMajor() {
        return major;
    }

    public void setMajor(String major) {
        this.major = major;
    }

    public double getScore() {
        return score;
    }

    public void setScore(double score) {
        this.score = score;
    }
}

public class User {
    private String username;
    private String password;

    // 构造函数
    public User(String username, String password) {
        this.username = username;
        this.password = password;
    }

    // getter和setter方法
    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

2. 用户登录界面模块

import java.util.Scanner;

public class Login {
    private String username;
    private String password;

    public void login() {
        Scanner input = new Scanner(System.in);
        System.out.println("请输入用户名：");
        username = input.nextLine();
        System.out.println("请输入密码：");
        password = input.nextLine();
        if (checkUser(username, password)) {
            System.out.println("登录成功！");
        } else {
            System.out.println("用户名或密码错误！");
        }
    }

    private boolean checkUser(String username, String password) {
        // 这里可以根据具体情况自定义用户的账号密码，例如：
        return username.equals("admin") && password.equals("123456");
    }
}

3. 学生信息管理主菜单界面模块

import java.util.Scanner;

public class MainMenu {
    private Scanner input = new Scanner(System.in);

    public void showMenu() {
        while (true) {
            System.out.println("请选择要执行的操作：");
            System.out.println("1. 学生信息添加");
            System.out.println("2. 学生信息修改");
            System.out.println("3. 学生信息删除");
            System.out.println("4. 学生信息查询");
            System.out.println("5. 用户信息查询");
            System.out.println("6. 用户密码修改");
            System.out.println("7. 退出程序");

            int choice = input.nextInt();
            switch (choice) {
                case 1:
                    addStudent();
                    break;
                case 2:
                    modifyStudent();
                    break;
                case 3:
                    deleteStudent();
                    break;
                case 4:
                    queryStudent();
                    break;
                case 5:
                    queryUser();
                    break;
                case 6:
                    modifyPassword();
                    break;
                case 7:
                    System.out.println("程序已退出！");
                    System.exit(0);
                default:
                    System.out.println("输入有误，请重新输入！");
                    break;
            }
        }
    }

    private void addStudent() {
        // 添加学生信息的代码
    }

    private void modifyStudent() {
        // 修改学生信息的代码
    }

    private void deleteStudent() {
        // 删除学生信息的代码
    }

    private void queryStudent() {
        // 查询学生信息的代码
    }

    private void queryUser() {
        // 查询用户信息的代码
    }

    private void modifyPassword() {
        // 修改密码的代码
    }
}

4. 学生信息添加模块

import java.util.ArrayList;
import java.util.Scanner;

public class AddStudent {
    private Scanner input = new Scanner(System.in);
    private ArrayList<Student> students;

    public AddStudent(ArrayList<Student> students) {
        this.students = students;
    }

    public void add() {
        System.out.println("请输入学生姓名：");
        String name = input.nextLine();
        System.out.println("请输入学生学号：");
        String id = input.nextLine();
        System.out.println("请输入学生性别：");
        String gender = input.nextLine();
        System.out.println("请输入学生专业：");
        String major = input.nextLine();
        System.out.println("请输入学生成绩：");
        double score = input.nextDouble();
        Student student = new Student(name, id, gender, major, score);
        students.add(student);
        System.out.println("学生信息添加成功！");
    }
}

5. 学生信息修改模块

import java.util.ArrayList;
import java.util.Scanner;

public class ModifyStudent {
    private Scanner input = new Scanner(System.in);
    private ArrayList<Student> students;

    public ModifyStudent(ArrayList<Student> students) {
        this.students = students;
    }

    public void modify() {
        System.out.println("请输入要修改的学生学号：");
        String id = input.nextLine();
        for (Student student : students) {
            if (student.getId().equals(id)) {
                System.out.println("请输入修改后的学生姓名（原值为" + student.getName() + "）：");
                String name = input.nextLine();
                System.out.println("请输入修改后的学生性别（原值为" + student.getGender() + "）：");
                String gender = input.nextLine();
                System.out.println("请输入修改后的学生专业（原值为" + student.getMajor() + "）：");
                String major = input.nextLine();
                System.out.println("请输入修改后的学生成绩（原值为" + student.getScore() + "）：");
                double score = input.nextDouble();
                student.setName(name);
                student.setGender(gender);
                student.setMajor(major);
                student.setScore(score);
                System.out.println("学生信息修改成功！");
                return;
            }
        }
        System.out.println("未找到该学生，请重新输入！");
    }
}

6. 学生信息删除模块

import java.util.ArrayList;
import java.util.Scanner;

public class DeleteStudent {
    private Scanner input = new Scanner(System.in);
    private ArrayList<Student> students;

    public DeleteStudent(ArrayList<Student> students) {
        this.students = students;
    }

    public void delete() {
        System.out.println("请输入要删除的学生学号：");
        String id = input.nextLine();
        for (Student student : students) {
            if (student.getId().equals(id)) {
                students.remove(student);
                System.out.println("学生信息删除成功！");
                return;
            }
        }
        System.out.println("未找到该学生，请重新输入！");
    }
}

7. 学生信息查询模块

import java.util.ArrayList;
import java.util.Scanner;

public class QueryStudent {
    private Scanner input = new Scanner(System.in);
    private ArrayList<Student> students;

    public QueryStudent(ArrayList<Student> students) {
        this.students = students;
    }

    public void query() {
        System.out.println("请选择要查询的方式：");
        System.out.println("1. 查询所有学生信息");
        System.out.println("2. 按学号查询学生信息");
        System.out.println("3. 按姓名查询学生信息");
        System.out.println("4. 按专业查询学生信息");
        System.out.println("5. 按成绩查询学生信息");

        int choice = input.nextInt();
        switch (choice) {
            case 1:
                showAll();
                break;
            case 2:
                queryById();
                break;
            case 3:
                queryByName();
                break;
            case 4:
                queryByMajor();
                break;
            case 5:
                queryByScore();
                break;
            default:
                System.out.println("输入有误，请重新输入！");
                break;
        }
    }

    private void showAll() {
        System.out.println("所有学生信息如下：");
        for (Student student : students) {
            System.out.println(student.getName() + " " + student.getId() + " " + student.getGender() + " " +
                    student.getMajor() + " " + student.getScore());
        }
    }

    private void queryById() {
        System.out.println("请输入要查询的学生学号：");
        String id = input.nextLine();
        for (Student student : students) {
            if (student.getId().equals(id)) {
                System.out.println(student.getName() + " " + student.getId() + " " + student.getGender() + " " +
                        student.getMajor() + " " + student.getScore());
                return;
            }
        }
        System.out.println("未找到该学生，请重新输入！");
    }

    private void queryByName() {
        System.out.println("请输入要查询的学生姓名：");
        String name = input.nextLine();
        for (Student student : students) {
            if (student.getName().equals(name)) {
                System.out.println(student.getName() + " " + student.getId() + " " + student.getGender() + " " +
                        student.getMajor() + " " + student.getScore());
            }
        }
    }

    private void queryByMajor() {
        System.out.println("请输入要查询的学生专业：");
        String major = input.nextLine();
        for (Student student : students) {
            if (student.getMajor().equals(major)) {
                System.out.println(student.getName() + " " + student.getId() + " " + student.getGender() + " " +
                        student.getMajor() + " " + student.getScore());
            }
        }
    }

    private void queryByScore() {
        System.out.println("请输入要查询的学生成绩（格式如60-80）：");
        double minScore = input.nextDouble();
        double maxScore = input.nextDouble();
        for (Student student : students) {
            if (student.getScore() >= minScore && student.getScore() <= maxScore) {
                System.out.println(student.getName() + " " + student.getId() + " " + student.getGender() + " " +
                        student.getMajor() + " " + student.getScore());
            }
        }
    }
}

8. 用户信息查询模块

public class QueryUser {
    private User user;

    public QueryUser(User user) {
        this.user = user;
    }

    public void query() {
        System.out.println("用户名：" + user.getUsername());
    }
}

9. 用户密码修改模块

import java.util.Scanner;

public class ModifyPassword {
    private Scanner input = new Scanner(System.in);
    private User user;

    public ModifyPassword(User user) {
        this.user = user;
    }

    public void modify() {
        System.out.println("请输入旧密码：");
        String oldPassword = input.nextLine();
        if (!oldPassword.equals(user.getPassword())) {
            System.out.println("密码错误！");
            return;
        }
        System.out.println("请输入新密码：");
        String newPassword = input.nextLine();
        user.setPassword(newPassword);
        System.out.println("密码修改成功！");
    }
}

最后，在主函数中调用以上模块即可：

import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        // 初始化用户和学生信息
        User user = new User("admin", "123456");
        ArrayList<Student> students = new ArrayList<>();
        students.add(new Student("张三", "1001", "男", "计算机科学与技术", 89.5));
        students.add(new Student("李四", "1002", "女", "软件工程", 92.0));
        students.add(new Student("王五", "1003", "男", "物联网工程", 85.5));

        // 用户登录
        Login login = new Login();
        login.login();

        // 显示主菜单
        MainMenu menu = new MainMenu();
        menu.showMenu();
    }
}