pattern

Behavioral pattern, template method.

definition

Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.

Frequency of use:  medium

 

 

UML class diagram

 

 

participants

    The classes and/or objects participating in this pattern are:

  • AbstractClass  (DataObject)
    • defines abstract primitive operations that concrete subclasses define to implement steps of an algorithm
    • implements a template method defining the skeleton of an algorithm. The template method calls primitive operations as well as operations defined in AbstractClass or those of other objects.
  • ConcreteClass  (CustomerDataObject)
    • implements the primitive operations ot carry out subclass-specific steps of the algorithm

 

 

sample code in C#

This structural code demonstrates the Template method which provides a skeleton calling sequence of methods. One or more steps can be deferred to subclasses which implement these steps without changing the overall calling sequence.



// Template pattern -- Structural example

using System;

namespace DoFactory.GangOfFour.Template.Structural
{
  
  // MainApp test application

  class MainApp
  {
    static void Main()
    {
      AbstractClass c;
      
      c = new ConcreteClassA();
      c.TemplateMethod();

      c = new ConcreteClassB();
      c.TemplateMethod();

      // Wait for user
      Console.Read();
    }
  }

  // "AbstractClass"

  abstract class AbstractClass
  {
    public abstract void PrimitiveOperation1();
    public abstract void PrimitiveOperation2();

    // The "Template method"
    public void TemplateMethod()
    {
      PrimitiveOperation1();
      PrimitiveOperation2();
      Console.WriteLine("");
    }
  }

  // "ConcreteClass"

  class ConcreteClassA : AbstractClass
  {
    public override void PrimitiveOperation1()
    {
      Console.WriteLine("ConcreteClassA.PrimitiveOperation1()");
    }
    public override void PrimitiveOperation2()
    {
      Console.WriteLine("ConcreteClassA.PrimitiveOperation2()");
    }
  }

  class ConcreteClassB : AbstractClass
  {
    public override void PrimitiveOperation1()
    {
      Console.WriteLine("ConcreteClassB.PrimitiveOperation1()");
    }
    public override void PrimitiveOperation2()
    {
      Console.WriteLine("ConcreteClassB.PrimitiveOperation2()");
    }
  }
}

Output
ConcreteClassA.PrimitiveOperation1()
ConcreteClassA.PrimitiveOperation2()



This real-world code demonstrates a Template method named Run() which provides a skeleton calling sequence of methods. Implementation of these steps are deferred to the CustomerDataObject subclass which implements the Connect, Select, Process, and Disconnect methods.



// Template pattern -- Real World example

using System;
using System.Data;
using System.Data.OleDb;

namespace DoFactory.GangOfFour.Template.RealWorld
{
  
  // MainApp test application

  class MainApp
  {
    static void Main()
    {
      DataAccessObject dao;
      
      dao = new Categories();
      dao.Run();

      dao = new Products();
      dao.Run();

      // Wait for user
      Console.Read();
    }
  }

  // "AbstractClass"

  abstract class DataAccessObject
  {
    protected string connectionString;

    protected DataSet dataSet;

    public virtual void Connect()
    {
      // Make sure mdb is on c:\
      connectionString =
        "provider=Microsoft.JET.OLEDB.4.0; " +
        "data source=c:\\nwind.mdb";
    }

    public abstract void Select();
    public abstract void Process();

    public virtual void Disconnect()
    {
      connectionString = "";
    }

    // The "Template Method"

    public void Run()
    {
      Connect();
      Select();
      Process();
      Disconnect();
    }
  }

  // "ConcreteClass"

  class Categories : DataAccessObject
  {
    public override void Select()
    {
      string sql = "select CategoryName from Categories";
      OleDbDataAdapter dataAdapter = new OleDbDataAdapter(
        sql, connectionString);

      dataSet = new DataSet();
      dataAdapter.Fill(dataSet, "Categories");
    }

    public override void Process()
    {
      Console.WriteLine("Categories ---- ");
      
      DataTable dataTable = dataSet.Tables["Categories"];
      foreach (DataRow row in dataTable.Rows)
      {
        Console.WriteLine(row["CategoryName"]);
      }
      Console.WriteLine();
    }
  }

  class Products : DataAccessObject
  {
    public override void Select()
    {
      string sql = "select ProductName from Products";
      OleDbDataAdapter dataAdapter = new OleDbDataAdapter(
        sql, connectionString);

      dataSet = new DataSet();
      dataAdapter.Fill(dataSet, "Products");
    }

    public override void Process()
    {
      Console.WriteLine("Products ---- ");
      DataTable dataTable = dataSet.Tables["Products"];
      foreach (DataRow row in dataTable.Rows)
      {
        Console.WriteLine(row["ProductName"]);
      }
      Console.WriteLine();
    }
  }
}

Output
Categories ----
Beverages
Condiments
Confections
Dairy Products
Grains/Cereals
Meat/Poultry
Produce
Seafood

Products ----
Chai
Chang
Aniseed Syrup
Chef Anton's Cajun Seasoning
Chef Anton's Gumbo Mix
Grandma's Boysenberry Spread
Uncle Bob's Organic Dried Pears
Northwoods Cranberry Sauce
Mishi Kobe Niku


21/02/2008 15:41:00 Publicado el por sigfrido Categoría Pattern Comentarios 0

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