用java和mysql做一个简单的系统

好的，我们可以做一个简单的学生管理系统。

首先，我们需要创建一个数据库，例如命名为`student_db`。

然后，我们需要创建一个名为`students`的表，用于存储学生的信息。

CREATE TABLE students (
  id INT NOT NULL AUTO_INCREMENT,
  name VARCHAR(50) NOT NULL,
  age INT NOT NULL,
  gender VARCHAR(10) NOT NULL,
  PRIMARY KEY (id)
);

接下来，我们可以使用Java编写一个简单的控制台应用程序，用于实现学生管理系统的基本功能，例如添加学生、修改学生、删除学生和查询学生信息等。

import java.sql.*;

public class StudentManagementSystem {
    private static final String URL = "jdbc:mysql://localhost:3306/student_db";
    private static final String USERNAME = "root";
    private static final String PASSWORD = "password";

    public static void main(String[] args) {
        try {
            Connection connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
            System.out.println("Connected to the database.");

            while (true) {
                System.out.println("Please select an option:");
                System.out.println("1. Add student");
                System.out.println("2. Modify student");
                System.out.println("3. Delete student");
                System.out.println("4. Query student");
                System.out.println("5. Exit");

                int option = Integer.parseInt(System.console().readLine());

                if (option == 1) {
                    System.out.println("Please enter the name of the student:");
                    String name = System.console().readLine();

                    System.out.println("Please enter the age of the student:");
                    int age = Integer.parseInt(System.console().readLine());

                    System.out.println("Please enter the gender of the student:");
                    String gender = System.console().readLine();

                    String sql = "INSERT INTO students (name, age, gender) VALUES (?, ?, ?)";

                    PreparedStatement statement = connection.prepareStatement(sql);
                    statement.setString(1, name);
                    statement.setInt(2, age);
                    statement.setString(3, gender);

                    int rowsInserted = statement.executeUpdate();

                    if (rowsInserted > 0) {
                        System.out.println("Student added successfully.");
                    }
                } else if (option == 2) {
                    System.out.println("Please enter the ID of the student:");
                    int id = Integer.parseInt(System.console().readLine());

                    System.out.println("Please enter the new name of the student:");
                    String name = System.console().readLine();

                    System.out.println("Please enter the new age of the student:");
                    int age = Integer.parseInt(System.console().readLine());

                    System.out.println("Please enter the new gender of the student:");
                    String gender = System.console().readLine();

                    String sql = "UPDATE students SET name = ?, age = ?, gender = ? WHERE id = ?";

                    PreparedStatement statement = connection.prepareStatement(sql);
                    statement.setString(1, name);
                    statement.setInt(2, age);
                    statement.setString(3, gender);
                    statement.setInt(4, id);

                    int rowsUpdated = statement.executeUpdate();

                    if (rowsUpdated > 0) {
                        System.out.println("Student updated successfully.");
                    }
                } else if (option == 3) {
                    System.out.println("Please enter the ID of the student:");
                    int id = Integer.parseInt(System.console().readLine());

                    String sql = "DELETE FROM students WHERE id = ?";

                    PreparedStatement statement = connection.prepareStatement(sql);
                    statement.setInt(1, id);

                    int rowsDeleted = statement.executeUpdate();

                    if (rowsDeleted > 0) {
                        System.out.println("Student deleted successfully.");
                    }
                } else if (option == 4) {
                    System.out.println("Please enter the ID of the student:");
                    int id = Integer.parseInt(System.console().readLine());

                    String sql = "SELECT * FROM students WHERE id = ?";

                    PreparedStatement statement = connection.prepareStatement(sql);
                    statement.setInt(1, id);

                    ResultSet resultSet = statement.executeQuery();

                    if (resultSet.next()) {
                        System.out.println("ID: " + resultSet.getInt("id"));
                        System.out.println("Name: " + resultSet.getString("name"));
                        System.out.println("Age: " + resultSet.getInt("age"));
                        System.out.println("Gender: " + resultSet.getString("gender"));
                    } else {
                        System.out.println("Student not found.");
                    }
                } else if (option == 5) {
                    System.out.println("Exiting the system...");
                    break;
                } else {
                    System.out.println("Invalid option.");
                }
            }

            connection.close();
            System.out.println("Disconnected from the database.");
        } catch (SQLException e) {
            System.out.println("SQL error occurred: " + e.getMessage());
        }
    }
}

这个程序的主要功能如下：

1. 连接到数据库
2. 提供用户界面，让用户选择要执行的操作
3. 根据用户选择的操作，执行相应的SQL语句
4. 处理SQL语句的执行结果
5. 关闭数据库连接

请注意，这只是一个简单的示例，实际应用程序可能需要更多的功能和更复杂的查询。此外，需要注意的是，为了使程序更健壮，需要添加适当的错误处理代码。