DatabaseConnection

// Product Interface: DatabaseConnection
interface DatabaseConnection {
    void connect();
    void disconnect();
}

// Concrete Products: MySqlConnection and PostgreSqlConnection
class MySqlConnection implements DatabaseConnection {
    @Override
    public void connect() {
        System.out.println("Connected to MySQL database");
        // MySQL-specific connection logic
    }

    @Override
    public void disconnect() {
        System.out.println("Disconnected from MySQL database");
        // MySQL-specific disconnection logic
    }
}

class PostgreSqlConnection implements DatabaseConnection {
    @Override
    public void connect() {
        System.out.println("Connected to PostgreSQL database");
        // PostgreSQL-specific connection logic
    }

    @Override
    public void disconnect() {
        System.out.println("Disconnected from PostgreSQL database");
        // PostgreSQL-specific disconnection logic
    }
}

// Factory Interface: DatabaseConnectionFactory
interface DatabaseConnectionFactory {
    DatabaseConnection createConnection();
}

// Concrete Factories: MySqlConnectionFactory and PostgreSqlConnectionFactory
class MySqlConnectionFactory implements DatabaseConnectionFactory {
    @Override
    public DatabaseConnection createConnection() {
        return new MySqlConnection();
    }
}

class PostgreSqlConnectionFactory implements DatabaseConnectionFactory {
    @Override
    public DatabaseConnection createConnection() {
        return new PostgreSqlConnection();
    }
}

// Client Code
public class DatabaseClient {
    public static void main(String[] args) {
        // Using a factory to create a MySQL database connection
        DatabaseConnectionFactory mySqlConnectionFactory = new MySqlConnectionFactory();
        DatabaseConnection mySqlConnection = mySqlConnectionFactory.createConnection();
        mySqlConnection.connect();
        mySqlConnection.disconnect();

        // Using a factory to create a PostgreSQL database connection
        DatabaseConnectionFactory postgreSqlConnectionFactory = new PostgreSqlConnectionFactory();
        DatabaseConnection postgreSqlConnection = postgreSqlConnectionFactory.createConnection();
        postgreSqlConnection.connect();
        postgreSqlConnection.disconnect();
    }
}

FactoryPattern

// Product Interface
interface Vehicle {
    void start();
    void stop();
}

// Concrete Products
class Car implements Vehicle {
    @Override
    public void start() {
        System.out.println("Car started.");
    }

    @Override
    public void stop() {
        System.out.println("Car stopped.");
    }
}

class ElectricCar implements Vehicle {
    @Override
    public void start() {
        System.out.println("Electric car started.");
    }

    @Override
    public void stop() {
        System.out.println("Electric car stopped.");
    }
}

// Factory Interface with Logic
interface VehicleFactory {
    Vehicle createVehicle(String fuelType);
}

// Concrete Factory with Logic
class VehicleFactoryImpl implements VehicleFactory {
    @Override
    public Vehicle createVehicle(String fuelType) {
        if ("Gasoline".equalsIgnoreCase(fuelType)) {
            return new Car();
        } else if ("Electric".equalsIgnoreCase(fuelType)) {
            return new ElectricCar();
        } else {
            throw new IllegalArgumentException("Invalid fuel type");
        }
    }
}

// Client
public class Client {
    public static void main(String[] args) {
        // Using the factory with logic to create a Gasoline-powered vehicle
        VehicleFactory vehicleFactory = new VehicleFactoryImpl();
        Vehicle gasolineCar = vehicleFactory.createVehicle("Gasoline");
        gasolineCar.start();
        gasolineCar.stop();

        // Using the factory with logic to create an Electric vehicle
        Vehicle electricCar = vehicleFactory.createVehicle("Electric");
        electricCar.start();
        electricCar.stop();
    }
}