运用java做一个学生登陆页面，进去后可以添加，删除，修改，查询学生成绩系统代码

好的，下面是一个简单的Java代码示例，实现了学生登陆页面和学生成绩系统的添加、删除、修改、查询功能。需要注意的是，这个示例代码仅供参考，实际应用中需要进行适当的修改和优化。

import java.sql.*;
import java.util.Scanner;

public class StudentGradeSystem {
    // 数据库连接相关信息
    private static final String DB_URL = "jdbc:mysql://localhost:3306/student_grade_system";
    private static final String DB_USER = "root";
    private static final String DB_PASSWORD = "123456";

    public static void main(String[] args) {
        // 学生登陆页面
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入用户名：");
        String username = scanner.nextLine();
        System.out.println("请输入密码：");
        String password = scanner.nextLine();
        if (!login(username, password)) {
            System.out.println("用户名或密码错误！");
            return;
        }

        // 学生成绩系统
        System.out.println("欢迎进入学生成绩系统！");
        while (true) {
            System.out.println("请选择操作：");
            System.out.println("1. 添加学生成绩");
            System.out.println("2. 删除学生成绩");
            System.out.println("3. 修改学生成绩");
            System.out.println("4. 查询学生成绩");
            System.out.println("5. 退出系统");

            int choice = scanner.nextInt();
            switch (choice) {
                case 1:
                    addGrade();
                    break;
                case 2:
                    deleteGrade();
                    break;
                case 3:
                    modifyGrade();
                    break;
                case 4:
                    queryGrade();
                    break;
                case 5:
                    System.out.println("感谢使用学生成绩系统！");
                    return;
                default:
                    System.out.println("无效的选择！");
            }
        }
    }

    // 学生登陆功能
    private static boolean login(String username, String password) {
        Connection connection = null;
        Statement statement = null;
        ResultSet resultSet = null;

        try {
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD);
            statement = connection.createStatement();
            String sql = "SELECT * FROM student WHERE username = '" + username + "' AND password = '" + password + "'";
            resultSet = statement.executeQuery(sql);
            return resultSet.next();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (resultSet != null) resultSet.close();
                if (statement != null) statement.close();
                if (connection != null) connection.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        return false;
    }

    // 添加学生成绩功能
    private static void addGrade() {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入学生姓名：");
        String name = scanner.nextLine();
        System.out.println("请输入学生学号：");
        String id = scanner.nextLine();
        System.out.println("请输入语文成绩：");
        double chinese = scanner.nextDouble();
        System.out.println("请输入数学成绩：");
        double math = scanner.nextDouble();
        System.out.println("请输入英语成绩：");
        double english = scanner.nextDouble();

        Connection connection = null;
        PreparedStatement preparedStatement = null;

        try {
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD);
            String sql = "INSERT INTO grade (name, id, chinese, math, english) VALUES (?, ?, ?, ?, ?)";
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, name);
            preparedStatement.setString(2, id);
            preparedStatement.setDouble(3, chinese);
            preparedStatement.setDouble(4, math);
            preparedStatement.setDouble(5, english);
            int result = preparedStatement.executeUpdate();
            if (result > 0) {
                System.out.println("添加成功！");
            } else {
                System.out.println("添加失败！");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (preparedStatement != null) preparedStatement.close();
                if (connection != null) connection.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    // 删除学生成绩功能
    private static void deleteGrade() {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入要删除的学生学号：");
        String id = scanner.nextLine();

        Connection connection = null;
        PreparedStatement preparedStatement = null;

        try {
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD);
            String sql = "DELETE FROM grade WHERE id = ?";
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, id);
            int result = preparedStatement.executeUpdate();
            if (result > 0) {
                System.out.println("删除成功！");
            } else {
                System.out.println("删除失败！");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (preparedStatement != null) preparedStatement.close();
                if (connection != null) connection.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    // 修改学生成绩功能
    private static void modifyGrade() {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入要修改的学生学号：");
        String id = scanner.nextLine();
        System.out.println("请输入新的语文成绩：");
        double chinese = scanner.nextDouble();
        System.out.println("请输入新的数学成绩：");
        double math = scanner.nextDouble();
        System.out.println("请输入新的英语成绩：");
        double english = scanner.nextDouble();

        Connection connection = null;
        PreparedStatement preparedStatement = null;

        try {
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD);
            String sql = "UPDATE grade SET chinese = ?, math = ?, english = ? WHERE id = ?";
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setDouble(1, chinese);
            preparedStatement.setDouble(2, math);
            preparedStatement.setDouble(3, english);
            preparedStatement.setString(4, id);
            int result = preparedStatement.executeUpdate();
            if (result > 0) {
                System.out.println("修改成功！");
            } else {
                System.out.println("修改失败！");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (preparedStatement != null) preparedStatement.close();
                if (connection != null) connection.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    // 查询学生成绩功能
    private static void queryGrade() {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入要查询的学生学号：");
        String id = scanner.nextLine();

        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;

        try {
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD);
            String sql = "SELECT * FROM grade WHERE id = ?";
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, id);
            resultSet = preparedStatement.executeQuery();
            if (resultSet.next()) {
                System.out.println("姓名：" + resultSet.getString("name"));
                System.out.println("学号：" + resultSet.getString("id"));
                System.out.println("语文成绩：" + resultSet.getDouble("chinese"));
                System.out.println("数学成绩：" + resultSet.getDouble("math"));
                System.out.println("英语成绩：" + resultSet.getDouble("english"));
            } else {
                System.out.println("查询失败！");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (resultSet != null) resultSet.close();
                if (preparedStatement != null) preparedStatement.close();
                if (connection != null) connection.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

上述代码中，我们使用了Java语言和MySQL数据库来实现学生成绩系统，其中包括了学生登陆页面和添加、删除、修改、查询学生成绩的功能。需要注意的是，该示例代码仅供参考，实际应用中需要进行适当的修改和优化。