用java代码写一份对mysql注册页面增删改查的代码

下面是一个基本的Java代码示例，用于在MySQL数据库中执行注册、查询、更新和删除操作。请注意，这只是一个基本示例，您需要根据自己的需求进行适当的更改和调整。

import java.sql.*;

public class MySQLExample {

    private Connection conn;
    private Statement stmt;
    private ResultSet rs;

    public MySQLExample() {
        try {
            // 连接数据库
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydatabase", "username", "password");
            stmt = conn.createStatement();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // 注册用户
    public void addUser(String username, String password, String email) {
        try {
            String sql = "INSERT INTO users (username, password, email) VALUES ('" + username + "', '" + password + "', '" + email + "')";
            stmt.executeUpdate(sql);
            System.out.println("User added successfully.");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // 查询用户
    public void getUser(String username) {
        try {
            String sql = "SELECT * FROM users WHERE username='" + username + "'";
            rs = stmt.executeQuery(sql);
            while (rs.next()) {
                String name = rs.getString("username");
                String password = rs.getString("password");
                String email = rs.getString("email");
                System.out.println("Name: " + name + ", Password: " + password + ", Email: " + email);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // 更新用户
    public void updateUser(String username, String password, String email) {
        try {
            String sql = "UPDATE users SET password='" + password + "', email='" + email + "' WHERE username='" + username + "'";
            stmt.executeUpdate(sql);
            System.out.println("User updated successfully.");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // 删除用户
    public void deleteUser(String username) {
        try {
            String sql = "DELETE FROM users WHERE username='" + username + "'";
            stmt.executeUpdate(sql);
            System.out.println("User deleted successfully.");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        MySQLExample example = new MySQLExample();
        example.addUser("John", "password", "john@example.com");
        example.getUser("John");
        example.updateUser("John", "newpassword", "newemail@example.com");
        example.deleteUser("John");
    }
}

请注意，这个示例只是一个基本的例子，您需要根据自己的需求进行适当的更改和调整。也要注意，上面的代码存在SQL注入的风险，您应该使用参数化查询来避免这种情况。