Design Pattern in .NET 101 - Factory Method Pattern (Creational Pattern)
By admin on Jan 12, 2008 in .NET, Creational, Programming
Factory Method Pattern defines an interface for creating an object, but let subclasses decide which class to instantiate. It lets a class defer instantiation to subclasses.
E.g., I defined a abstract News class.
using System;
using System.Collections.Generic;
using System.Text;
namespace FactoryPattern
{
abstract class News
{
}
}
Different kinds of news are defined..
using System;
using System.Collections.Generic;
using System.Text;
namespace FactoryPattern
{
class AdNews:News
{
}
}
using System;
using System.Collections.Generic;
using System.Text;
namespace FactoryPattern
{
class FashionNews:News
{
}
}
using System;
using System.Collections.Generic;
using System.Text;
namespace FactoryPattern
{
class FinanceNews:News
{
}
}
using System;
using System.Collections.Generic;
using System.Text;
namespace FactoryPattern
{
class SportsNews:News
{
}
}
using System;
using System.Collections.Generic;
using System.Text;
namespace FactoryPattern
{
class WorldNews:News
{
}
}
I defined the abstract factory class, Publication
using System;
using System.Collections.Generic;
using System.Text;
using System.Collections;
namespace FactoryPattern
{
abstract class Publication
{
private ArrayList publishedNews = new ArrayList();
// Constructor calls abstract Factory method
public Publication()
{
this.PublishNews();
}
public ArrayList PublishedNews
{
get
{
return publishedNews;
}
}
// Factory Method
public abstract void PublishNews();
}
}
In the Publication class, the factory method is called, but it is not implemented yet.
Newspaper and FashionMagazine extends Publication class.
using System;
using System.Collections.Generic;
using System.Text;
namespace FactoryPattern
{
class NewsPaper:Publication
{
public override void PublishNews()
{
this.PublishedNews.Add(new AdNews());
this.PublishedNews.Add(new FashionNews());
this.PublishedNews.Add(new WorldNews());
this.PublishedNews.Add(new SportsNews());
this.PublishedNews.Add(new FinanceNews());
}
}
}
using System;
using System.Collections.Generic;
using System.Text;
namespace FactoryPattern
{
class FashionMagazine:Publication
{
public override void PublishNews()
{
this.PublishedNews.Add(new AdNews());
this.PublishedNews.Add(new FashionNews());
}
}
}
To test it
using System;
using System.Collections.Generic;
using System.Text;
namespace FactoryPattern
{
class Program
{
static void Main(string[] args)
{
Publication newsPaper = new NewsPaper();
Console.WriteLine(newsPaper.GetType().Name);
foreach (News news in newsPaper.PublishedNews)
{
Console.WriteLine("-" + news.GetType().Name);
}
Console.WriteLine();
Publication fashionMagazine = new FashionMagazine();
Console.WriteLine(fashionMagazine.GetType().Name);
foreach (News news in fashionMagazine.PublishedNews)
{
Console.WriteLine("-" + news.GetType().Name);
}
Console.Read();
}
}
}
The output
NewsPaper -AdNews -FashionNews -WorldNews -SportsNews -FinanceNews FashionMagazine -AdNews -FashionNews