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Template Method

Template Method em C#

O Template Method é um padrão de projeto comportamental que permite definir o esqueleto de um algoritmo em uma classe base e permitir que as subclasses substituam as etapas sem alterar a estrutura geral do algoritmo.

Complexidade:

Popularidade:

Exemplos de uso: O padrão Template Method é bastante comum nos frameworks C#. Os desenvolvedores costumam usá-lo para fornecer aos usuários do framework um meio simples de estender a funcionalidade padrão usando herança.

Identificação: O Template Method pode ser reconhecido por métodos comportamentais que já possuem um comportamento “padrão” definido pela classe base.

Exemplo conceitual

Este exemplo ilustra a estrutura do padrão de projeto Template Method. Ele se concentra em responder a estas perguntas:

  • De quais classes ele consiste?
  • Quais papéis essas classes desempenham?
  • De que maneira os elementos do padrão estão relacionados?

Program.cs: Exemplo conceitual

using System;

namespace RefactoringGuru.DesignPatterns.TemplateMethod.Conceptual
{
    // The Abstract Class defines a template method that contains a skeleton of
    // some algorithm, composed of calls to (usually) abstract primitive
    // operations.
    //
    // Concrete subclasses should implement these operations, but leave the
    // template method itself intact.
    abstract class AbstractClass
    {
        // The template method defines the skeleton of an algorithm.
        public void TemplateMethod()
        {
            this.BaseOperation1();
            this.RequiredOperations1();
            this.BaseOperation2();
            this.Hook1();
            this.RequiredOperation2();
            this.BaseOperation3();
            this.Hook2();
        }

        // These operations already have implementations.
        protected void BaseOperation1()
        {
            Console.WriteLine("AbstractClass says: I am doing the bulk of the work");
        }

        protected void BaseOperation2()
        {
            Console.WriteLine("AbstractClass says: But I let subclasses override some operations");
        }

        protected void BaseOperation3()
        {
            Console.WriteLine("AbstractClass says: But I am doing the bulk of the work anyway");
        }
        
        // These operations have to be implemented in subclasses.
        protected abstract void RequiredOperations1();

        protected abstract void RequiredOperation2();
        
        // These are "hooks." Subclasses may override them, but it's not
        // mandatory since the hooks already have default (but empty)
        // implementation. Hooks provide additional extension points in some
        // crucial places of the algorithm.
        protected virtual void Hook1() { }

        protected virtual void Hook2() { }
    }

    // Concrete classes have to implement all abstract operations of the base
    // class. They can also override some operations with a default
    // implementation.
    class ConcreteClass1 : AbstractClass
    {
        protected override void RequiredOperations1()
        {
            Console.WriteLine("ConcreteClass1 says: Implemented Operation1");
        }

        protected override void RequiredOperation2()
        {
            Console.WriteLine("ConcreteClass1 says: Implemented Operation2");
        }
    }

    // Usually, concrete classes override only a fraction of base class'
    // operations.
    class ConcreteClass2 : AbstractClass
    {
        protected override void RequiredOperations1()
        {
            Console.WriteLine("ConcreteClass2 says: Implemented Operation1");
        }

        protected override void RequiredOperation2()
        {
            Console.WriteLine("ConcreteClass2 says: Implemented Operation2");
        }

        protected override void Hook1()
        {
            Console.WriteLine("ConcreteClass2 says: Overridden Hook1");
        }
    }

    class Client
    {
        // The client code calls the template method to execute the algorithm.
        // Client code does not have to know the concrete class of an object it
        // works with, as long as it works with objects through the interface of
        // their base class.
        public static void ClientCode(AbstractClass abstractClass)
        {
            // ...
            abstractClass.TemplateMethod();
            // ...
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Same client code can work with different subclasses:");

            Client.ClientCode(new ConcreteClass1());

            Console.Write("\n");
            
            Console.WriteLine("Same client code can work with different subclasses:");
            Client.ClientCode(new ConcreteClass2());
        }
    }
}

Output.txt: Resultados da execução

Same client code can work with different subclasses:
AbstractClass says: I am doing the bulk of the work
ConcreteClass1 says: Implemented Operation1
AbstractClass says: But I let subclasses override some operations
ConcreteClass1 says: Implemented Operation2
AbstractClass says: But I am doing the bulk of the work anyway

Same client code can work with different subclasses:
AbstractClass says: I am doing the bulk of the work
ConcreteClass2 says: Implemented Operation1
AbstractClass says: But I let subclasses override some operations
ConcreteClass2 says: Overridden Hook1
ConcreteClass2 says: Implemented Operation2
AbstractClass says: But I am doing the bulk of the work anyway

Template Method em outras linguagens

Template Method em C++ Template Method em Go Template Method em Java Template Method em PHP Template Method em Python Template Method em Ruby Template Method em Rust Template Method em Swift Template Method em TypeScript