C# Example

// Abstract Factory Design Pattern
//
// Intent: Lets you produce families of related objects without specifying their
// concrete classes.

using System;

namespace RefactoringGuru.DesignPatterns.AbstractFactory.Conceptual
{
    // The Abstract Factory interface declares a set of methods that return
    // different abstract products. These products are called a family and are
    // related by a high-level theme or concept. Products of one family are
    // usually able to collaborate among themselves. A family of products may
    // have several variants, but the products of one variant are incompatible
    // with products of another.
    public interface IAbstractFactory
    {
        IAbstractProductA CreateProductA();

        IAbstractProductB CreateProductB();
    }

    // Concrete Factories produce a family of products that belong to a single
    // variant. The factory guarantees that resulting products are compatible.
    // Note that signatures of the Concrete Factory's methods return an abstract
    // product, while inside the method a concrete product is instantiated.
    class ConcreteFactory1 : IAbstractFactory
    {
        public IAbstractProductA CreateProductA()
        {
            return new ConcreteProductA1();
        }

        public IAbstractProductB CreateProductB()
        {
            return new ConcreteProductB1();
        }
    }

    // Each Concrete Factory has a corresponding product variant.
    class ConcreteFactory2 : IAbstractFactory
    {
        public IAbstractProductA CreateProductA()
        {
            return new ConcreteProductA2();
        }

        public IAbstractProductB CreateProductB()
        {
            return new ConcreteProductB2();
        }
    }

    // Each distinct product of a product family should have a base interface.
    // All variants of the product must implement this interface.
    public interface IAbstractProductA
    {
        string UsefulFunctionA();
    }

    // Concrete Products are created by corresponding Concrete Factories.
    class ConcreteProductA1 : IAbstractProductA
    {
        public string UsefulFunctionA()
        {
            return "The result of the product A1.";
        }
    }

    class ConcreteProductA2 : IAbstractProductA
    {
        public string UsefulFunctionA()
        {
            return "The result of the product A2.";
        }
    }

    // Here's the the base interface of another product. All products can
    // interact with each other, but proper interaction is possible only between
    // products of the same concrete variant.
    public interface IAbstractProductB
    {
        // Product B is able to do its own thing...
        string UsefulFunctionB();

        // ...but it also can collaborate with the ProductA.
        //
        // The Abstract Factory makes sure that all products it creates are of
        // the same variant and thus, compatible.
        string AnotherUsefulFunctionB(IAbstractProductA collaborator);
    }

    // Concrete Products are created by corresponding Concrete Factories.
    class ConcreteProductB1 : IAbstractProductB
    {
        public string UsefulFunctionB()
        {
            return "The result of the product B1.";
        }

        // The variant, Product B1, is only able to work correctly with the
        // variant, Product A1. Nevertheless, it accepts any instance of
        // AbstractProductA as an argument.
        public string AnotherUsefulFunctionB(IAbstractProductA collaborator)
        {
            var result = collaborator.UsefulFunctionA();

            return $"The result of the B1 collaborating with the ({result})";
        }
    }

    class ConcreteProductB2 : IAbstractProductB
    {
        public string UsefulFunctionB()
        {
            return "The result of the product B2.";
        }

       // The variant, Product B2, is only able to work correctly with the
       // variant, Product A2. Nevertheless, it accepts any instance of
       // AbstractProductA as an argument.
        public string AnotherUsefulFunctionB(IAbstractProductA collaborator)
        {
            var result = collaborator.UsefulFunctionA();

            return $"The result of the B2 collaborating with the ({result})";
        }
    }

    // The client code works with factories and products only through abstract
    // types: AbstractFactory and AbstractProduct. This lets you pass any
    // factory or product subclass to the client code without breaking it.
    class Client
    {
        public void Main()
        {
            // The client code can work with any concrete factory class.
            Console.WriteLine("Client: Testing client code with the first factory type...");
            ClientMethod(new ConcreteFactory1());
            Console.WriteLine();

            Console.WriteLine("Client: Testing the same client code with the second factory type...");
            ClientMethod(new ConcreteFactory2());
        }

        public void ClientMethod(IAbstractFactory factory)
        {
            var productA = factory.CreateProductA();
            var productB = factory.CreateProductB();

            Console.WriteLine(productB.UsefulFunctionB());
            Console.WriteLine(productB.AnotherUsefulFunctionB(productA));
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            new Client().Main();
        }
    }
}

Client: Testing client code with the first factory type...
The result of the product B1.
The result of the B1 collaborating with the (The result of the product A1.)

Client: Testing the same client code with the second factory type...
The result of the product B2.
The result of the B2 collaborating with the (The result of the product A2.)