Editing Combined Patterns New

Mediator


Objective

Define an object that encapsulates the interaction between others, promoting a low coupling; since it prevents objects from explicitly referencing each other by varying independently of their interaction.

Function

Define an object that coordinates communication between others of different kinds, but that functions as a whole.

Structure

As shown in figure 1

  • Client: Component that initiates communication with the rest of the components through the mediator.

  • Components: Components that are part of the communication network through the mediator, these can be various objects that share the same mediator to communicate.

  • Mediator: Component that serves as a mediator between the rest of the components, its main role is to channel the incoming messages to the corresponding recipient.

The structure that meets this pattern is shown in Figure 1

Responsive image

Figure 1: UML Diagram Mediator Pattern

Applications

The use of the Mediator pattern is recommended when:

  • The objects of the application communicate in a well-structured but potentially complex way.

  • The identities of objects must be protected even when they communicate with each other.

  • El comportamiento de algunos objetos puede ser agrupado y personalizado.

  • The reuse of an object is complicated because this reference and communicates with many other objects.

Design Patterns Collaborators

  • Mediator classes frequently use the Observer design pattern to receive notifications of different requests from interacting classes.

  • You can use the Adapter pattern to make the Mediator class independent of the specific classes it manages.

Scope of action

Applied at the object level.

Problem

All object-oriented applications base their operation on the interaction between objects. If there is no clearly defined mechanism of interaction, a highly coupled application can be generated, contradicting the principles of object-oriented programming.

Solution

The Mediator design pattern coordinates interactions between related objects; centralizing in one class the logic that performs the state changes of the objects, so that it offers a systematized way to increase cohesion (the logic is centralized) and reduce the coupling between classes (the dependencies between them are reduced).

Diagram or Implementation

Responsive image

Figure 2: UML Diagram Mediator Pattern

Figure 2 explains the behaviour of the pattern by means of a sequence diagram.

  • The class ComponentA wants to communicate with ComponentB and sends it a message via the mediator.

  • The componete mediator can analyze the message for debugging purposes, tracking or to channel the message to the recipient.

  • The message is delivered to the recipient and returns a response to the mediator component.

  • The mediator receives the response and redirects it to ComponentA.

  • Similarly, the process can be repeated from ComponentB to ComponentA by repeating the previous steps achieving two-way communication.


Implementations of the Mediator pattern:

    	
    		
from __future__ import annotations
from abc import ABC, abstractmethod, abstractproperty
from typing import Any


class Builder(ABC):
    """
    The Builder interface specifies methods for creating the different parts of
    the Product objects.
    """

    @abstractproperty
    def product(self) -> None:
        pass

    @abstractmethod
    def produce_part_a(self) -> None:
        pass

    @abstractmethod
    def produce_part_b(self) -> None:
        pass

    @abstractmethod
    def produce_part_c(self) -> None:
        pass


class ConcreteBuilder1(Builder):
    """
    The Concrete Builder classes follow the Builder interface and provide
    specific implementations of the building steps. Your program may have
    several variations of Builders, implemented differently.
    """

    def __init__(self) -> None:
        """
        A fresh builder instance should contain a blank product object, which is
        used in further assembly.
        """
        self.reset()

    def reset(self) -> None:
        self._product = Product1()

    @property
    def product(self) -> Product1:
        """
        Concrete Builders are supposed to provide their own methods for
        retrieving results. That's because various types of builders may create
        entirely different products that don't follow the same interface.
        Therefore, such methods cannot be declared in the base Builder interface
        (at least in a statically typed programming language).

        Usually, after returning the end result to the client, a builder
        instance is expected to be ready to start producing another product.
        That's why it's a usual practice to call the reset method at the end of
        the `getProduct` method body. However, this behavior is not mandatory,
        and you can make your builders wait for an explicit reset call from the
        client code before disposing of the previous result.
        """
        product = self._product
        self.reset()
        return product

    def produce_part_a(self) -> None:
        self._product.add("PartA1")

    def produce_part_b(self) -> None:
        self._product.add("PartB1")

    def produce_part_c(self) -> None:
        self._product.add("PartC1")


class Product1():
    """
    It makes sense to use the Builder pattern only when your products are quite
    complex and require extensive configuration.

    Unlike in other creational patterns, different concrete builders can produce
    unrelated products. In other words, results of various builders may not
    always follow the same interface.
    """

    def __init__(self) -> None:
        self.parts = []

    def add(self, part: Any) -> None:
        self.parts.append(part)

    def list_parts(self) -> None:
        print(f"Product parts: {', '.join(self.parts)}", end="")


class Director:
    """
    The Director is only responsible for executing the building steps in a
    particular sequence. It is helpful when producing products according to a
    specific order or configuration. Strictly speaking, the Director class is
    optional, since the client can control builders directly.
    """

    def __init__(self) -> None:
        self._builder = None

    @property
    def builder(self) -> Builder:
        return self._builder

    @builder.setter
    def builder(self, builder: Builder) -> None:
        """
        The Director works with any builder instance that the client code passes
        to it. This way, the client code may alter the final type of the newly
        assembled product.
        """
        self._builder = builder

    """
    The Director can construct several product variations using the same
    building steps.
    """

    def build_minimal_viable_product(self) -> None:
        self.builder.produce_part_a()

    def build_full_featured_product(self) -> None:
        self.builder.produce_part_a()
        self.builder.produce_part_b()
        self.builder.produce_part_c()


if __name__ == "__main__":
    """
    The client code creates a builder object, passes it to the director and then
    initiates the construction process. The end result is retrieved from the
    builder object.
    """

    director = Director()
    builder = ConcreteBuilder1()
    director.builder = builder

    print("Standard basic product: ")
    director.build_minimal_viable_product()
    builder.product.list_parts()

    print("\n")

    print("Standard full featured product: ")
    director.build_full_featured_product()
    builder.product.list_parts()

    print("\n")

    # Remember, the Builder pattern can be used without a Director class.
    print("Custom product: ")
    builder.produce_part_a()
    builder.produce_part_b()
    builder.product.list_parts()    	
    	
    	
    		
namespace RefactoringGuru\Builder\Conceptual;

/**
 * The Builder interface specifies methods for creating the different parts of
 * the Product objects.
 */
interface Builder
{
    public function producePartA(): void;

    public function producePartB(): void;

    public function producePartC(): void;
}

/**
 * The Concrete Builder classes follow the Builder interface and provide
 * specific implementations of the building steps. Your program may have several
 * variations of Builders, implemented differently.
 */
class ConcreteBuilder1 implements Builder
{
    private $product;

    /**
     * A fresh builder instance should contain a blank product object, which is
     * used in further assembly.
     */
    public function __construct()
    {
        $this->reset();
    }

    public function reset(): void
    {
        $this->product = new Product1();
    }

    /**
     * All production steps work with the same product instance.
     */
    public function producePartA(): void
    {
        $this->product->parts[] = "PartA1";
    }

    public function producePartB(): void
    {
        $this->product->parts[] = "PartB1";
    }

    public function producePartC(): void
    {
        $this->product->parts[] = "PartC1";
    }

    /**
     * Concrete Builders are supposed to provide their own methods for
     * retrieving results. That's because various types of builders may create
     * entirely different products that don't follow the same interface.
     * Therefore, such methods cannot be declared in the base Builder interface
     * (at least in a statically typed programming language). Note that PHP is a
     * dynamically typed language and this method CAN be in the base interface.
     * However, we won't declare it there for the sake of clarity.
     *
     * Usually, after returning the end result to the client, a builder instance
     * is expected to be ready to start producing another product. That's why
     * it's a usual practice to call the reset method at the end of the
     * `getProduct` method body. However, this behavior is not mandatory, and
     * you can make your builders wait for an explicit reset call from the
     * client code before disposing of the previous result.
     */
    public function getProduct(): Product1
    {
        $result = $this->product;
        $this->reset();

        return $result;
    }
}

/**
 * It makes sense to use the Builder pattern only when your products are quite
 * complex and require extensive configuration.
 *
 * Unlike in other creational patterns, different concrete builders can produce
 * unrelated products. In other words, results of various builders may not
 * always follow the same interface.
 */
class Product1
{
    public $parts = [];

    public function listParts(): void
    {
        echo "Product parts: " . implode(', ', $this->parts) . "\n\n";
    }
}

/**
 * The Director is only responsible for executing the building steps in a
 * particular sequence. It is helpful when producing products according to a
 * specific order or configuration. Strictly speaking, the Director class is
 * optional, since the client can control builders directly.
 */
class Director
{
    /**
     * @var Builder
     */
    private $builder;

    /**
     * The Director works with any builder instance that the client code passes
     * to it. This way, the client code may alter the final type of the newly
     * assembled product.
     */
    public function setBuilder(Builder $builder): void
    {
        $this->builder = $builder;
    }

    /**
     * The Director can construct several product variations using the same
     * building steps.
     */
    public function buildMinimalViableProduct(): void
    {
        $this->builder->producePartA();
    }

    public function buildFullFeaturedProduct(): void
    {
        $this->builder->producePartA();
        $this->builder->producePartB();
        $this->builder->producePartC();
    }
}

/**
 * The client code creates a builder object, passes it to the director and then
 * initiates the construction process. The end result is retrieved from the
 * builder object.
 */
function clientCode(Director $director)
{
    $builder = new ConcreteBuilder1();
    $director->setBuilder($builder);

    echo "Standard basic product:\n";
    $director->buildMinimalViableProduct();
    $builder->getProduct()->listParts();

    echo "Standard full featured product:\n";
    $director->buildFullFeaturedProduct();
    $builder->getProduct()->listParts();

    // Remember, the Builder pattern can be used without a Director class.
    echo "Custom product:\n";
    $builder->producePartA();
    $builder->producePartC();
    $builder->getProduct()->listParts();
}

$director = new Director();
clientCode($director);    	
    	
    	
    		
/* "Product" */
class Pizza {
    private String dough = "";
    private String sauce = "";
    private String topping = "";

    public void setDough(String dough) {
        this.dough = dough;
    }

    public void setSauce(String sauce) {
        this.sauce = sauce;
    }

    public void setTopping(String topping) {
        this.topping = topping;
    }
}

/* "Abstract Builder" */
abstract class PizzaBuilder {
    protected Pizza pizza;

    public Pizza getPizza() {
        return pizza;
    }

    public void createNewPizzaProduct() {
        pizza = new Pizza();
    }

    public abstract void buildDough();
    public abstract void buildSauce();
    public abstract void buildTopping();
}

/* "ConcreteBuilder" */
class HawaiianPizzaBuilder extends PizzaBuilder {
    public void buildDough() {
        pizza.setDough("cross");
    }

    public void buildSauce() {
        pizza.setSauce("mild");
    }

    public void buildTopping() {
        pizza.setTopping("ham+pineapple");
    }
}

/* "ConcreteBuilder" */
class SpicyPizzaBuilder extends PizzaBuilder {
    public void buildDough() {
        pizza.setDough("pan baked");
    }

    public void buildSauce() {
        pizza.setSauce("hot");
    }

    public void buildTopping() {
        pizza.setTopping("pepperoni+salami");
    }
}

/* "Director" */
class Waiter {
    private PizzaBuilder pizzaBuilder;

    public void setPizzaBuilder(PizzaBuilder pb) {
        pizzaBuilder = pb;
    }

    public Pizza getPizza() {
        return pizzaBuilder.getPizza();
    }

    public void constructPizza() {
        pizzaBuilder.createNewPizzaProduct();
        pizzaBuilder.buildDough();
        pizzaBuilder.buildSauce();
        pizzaBuilder.buildTopping();
    }
}

/* A customer ordering a pizza. */
public class PizzaBuilderDemo {
    public static void main(String[] args) {
        Waiter waiter = new Waiter();
        PizzaBuilder hawaiianPizzabuilder = new HawaiianPizzaBuilder();
        PizzaBuilder spicyPizzaBuilder = new SpicyPizzaBuilder();

        waiter.setPizzaBuilder( hawaiianPizzabuilder );
        waiter.constructPizza();

        Pizza pizza = waiter.getPizza();
    }
}