使用Java和mysql写一个空调收费系统

好的，我可以为您提供一些思路和代码示例。

首先，您需要创建一个名为"air_conditioning"的数据库，其中包含两个表：一个是"users"表，用于存储用户信息，另一个是"charges"表，用于记录用户的空调使用情况和收费信息。

以下是创建这两个表的SQL语句：

CREATE TABLE users (
  id INT NOT NULL AUTO_INCREMENT,
  name VARCHAR(50) NOT NULL,
  balance DECIMAL(10,2) NOT NULL,
  PRIMARY KEY (id)
);

CREATE TABLE charges (
  id INT NOT NULL AUTO_INCREMENT,
  user_id INT NOT NULL,
  start_time DATETIME NOT NULL,
  end_time DATETIME NOT NULL,
  cost DECIMAL(10,2) NOT NULL,
  PRIMARY KEY (id),
  FOREIGN KEY (user_id) REFERENCES users(id)
);

接下来，您需要编写Java代码来连接数据库并实现收费系统的功能。以下是一个简单的示例：

import java.sql.*;

public class AirConditioningSystem {
    private static final String DB_URL = "jdbc:mysql://localhost/air_conditioning";
    private static final String DB_USER = "root";
    private static final String DB_PASSWORD = "password";

    public static void main(String[] args) {
        try {
            Connection conn = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD);
            System.out.println("Connected to database");

            // 用户充值
            recharge(conn, 1, 100.00);

            // 用户使用空调
            useAirConditioning(conn, 1);

            // 查询用户余额和使用记录
            queryUser(conn, 1);

            conn.close();
            System.out.println("Disconnected from database");
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    // 用户充值
    public static void recharge(Connection conn, int userId, double amount) throws SQLException {
        String sql = "UPDATE users SET balance = balance + ? WHERE id = ?";
        PreparedStatement stmt = conn.prepareStatement(sql);
        stmt.setDouble(1, amount);
        stmt.setInt(2, userId);
        stmt.executeUpdate();
        System.out.println("User " + userId + " has recharged " + amount + " yuan");
    }

    // 用户使用空调
    public static void useAirConditioning(Connection conn, int userId) throws SQLException {
        // 检查用户余额
        String sql1 = "SELECT balance FROM users WHERE id = ?";
        PreparedStatement stmt1 = conn.prepareStatement(sql1);
        stmt1.setInt(1, userId);
        ResultSet rs1 = stmt1.executeQuery();
        if (!rs1.next()) {
            System.out.println("User " + userId + " not found");
            return;
        }
        double balance = rs1.getDouble("balance");
        if (balance < 1.00) {
            System.out.println("User " + userId + " has insufficient balance");
            return;
        }

        // 记录空调使用情况和费用
        String sql2 = "INSERT INTO charges (user_id, start_time, end_time, cost) VALUES (?, NOW(), NOW() + INTERVAL 1 HOUR, 1.00)";
        PreparedStatement stmt2 = conn.prepareStatement(sql2);
        stmt2.setInt(1, userId);
        stmt2.executeUpdate();

        // 扣除费用
        String sql3 = "UPDATE users SET balance = balance - 1.00 WHERE id = ?";
        PreparedStatement stmt3 = conn.prepareStatement(sql3);
        stmt3.setInt(1, userId);
        stmt3.executeUpdate();

        System.out.println("User " + userId + " has used the air conditioning");
    }

    // 查询用户余额和使用记录
    public static void queryUser(Connection conn, int userId) throws SQLException {
        String sql1 = "SELECT name, balance FROM users WHERE id = ?";
        PreparedStatement stmt1 = conn.prepareStatement(sql1);
        stmt1.setInt(1, userId);
        ResultSet rs1 = stmt1.executeQuery();
        if (!rs1.next()) {
            System.out.println("User " + userId + " not found");
            return;
        }
        String name = rs1.getString("name");
        double balance = rs1.getDouble("balance");
        System.out.println("User " + userId + " (" + name + ") has a balance of " + balance + " yuan");

        String sql2 = "SELECT start_time, end_time, cost FROM charges WHERE user_id = ?";
        PreparedStatement stmt2 = conn.prepareStatement(sql2);
        stmt2.setInt(1, userId);
        ResultSet rs2 = stmt2.executeQuery();
        while (rs2.next()) {
            Timestamp startTime = rs2.getTimestamp("start_time");
            Timestamp endTime = rs2.getTimestamp("end_time");
            double cost = rs2.getDouble("cost");
            System.out.println("  Usage: " + startTime + " - " + endTime + ", cost " + cost + " yuan");
        }
    }
}

上述代码演示了用户充值、使用空调和查询余额和使用记录的功能。您可以根据需要进行修改和扩展。

希望这可以帮助您开始编写空调收费系统。