给我一个jdbc的增删改查案例

好的，下面是一个简单的 JDBC 增删改查案例：

首先，我们需要获取数据库连接。

import java.sql.*;

public class JdbcExample {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/mydatabase";  // 数据库的地址
        String username = "root";  // 数据库用户名
        String password = "password";  // 数据库密码

        try (Connection conn = DriverManager.getConnection(url, username, password)) {
            System.out.println("数据库连接成功！");

            // 后面可以进行增删改查的操作
        } catch (SQLException e) {
            System.out.println("数据库连接失败：" + e.getMessage());
        }
    }
}

接下来，我们可以进行增删改查的操作。

// 插入数据
try (Statement stmt = conn.createStatement()) {
    String sql = "INSERT INTO users (username, password, age) VALUES ('Tom', 'password123', 21)";
    int rowsAffected = stmt.executeUpdate(sql);
    System.out.println("插入数据成功！影响了 " + rowsAffected + " 行数据。");
} catch (SQLException e) {
    System.out.println("插入数据失败：" + e.getMessage());
}

// 更新数据
try (Statement stmt = conn.createStatement()) {
    String sql = "UPDATE users SET age = 22 WHERE username = 'Tom'";
    int rowsAffected = stmt.executeUpdate(sql);
    System.out.println("更新数据成功！影响了 " + rowsAffected + " 行数据。");
} catch (SQLException e) {
    System.out.println("更新数据失败：" + e.getMessage());
}

// 删除数据
try (Statement stmt = conn.createStatement()) {
    String sql = "DELETE FROM users WHERE username = 'Tom'";
    int rowsAffected = stmt.executeUpdate(sql);
    System.out.println("删除数据成功！影响了 " + rowsAffected + " 行数据。");
} catch (SQLException e) {
    System.out.println("删除数据失败：" + e.getMessage());
}

// 查询数据
try (Statement stmt = conn.createStatement();
     ResultSet rs = stmt.executeQuery("SELECT * FROM users")) {
    while (rs.next()) {
        int id = rs.getInt("id");
        String username = rs.getString("username");
        String password = rs.getString("password");
        int age = rs.getInt("age");
        System.out.println("id: " + id + ", username: " + username + ", password: " + password + ", age: " + age);
    }
} catch (SQLException e) {
    System.out.println("查询数据失败：" + e.getMessage());
}

以上就是一个简单的 JDBC 增删改查案例。