Design Patterns-Creational

Design Patterns

Pattern is something that occurs in a definite order. Sometimes we use a particular way to tackle a problem and that becomes a Pattern.

In technical terms, the design patterns are language-independent strategies for solving common object-oriented design problems. Design patterns represent the best practices and it should be used in the development to provide common solution to a specific problem.

Why should we use design patterns?

·         It provides some popular solutions to coding problems.

·         Learning design patterns speeds up your experience accumulation in OOA/OOD.

·         Design patterns describe how objects communicate without become entangled in each other’s data models and methods. For an example:-

Each of these aspects of the problem is a separate object and each hasIts own rules for managing its data. Communication between the user, the GUI and the data should be carefully controlled.

·         Design patterns provide a standard terminology and are specific to particular scenario. For example, a singleton design pattern signifies use of single object so all developers familiar with single design pattern will make use of single object and they can tell each other that program is following a singleton pattern.

Creational Patterns

 These are ones that create objects for you, rather than having you instantiate objects directly. This gives  your program more flexibility in deciding which objects need to be created for a given case.

Creational Patterns can be categorized as:

Factory Pattern

In factory pattern, we create object without exposing the creation logic to the client and refer to newly  created object using a common interface.

In simple words, if we have a super class and n sub-classes, and based on data provided, we have to   return the object of one of the sub-classes, we use a factory pattern.

Real Life Example

I just love to eat and I believe many of us like to try different cuisines. Don’t get confused I am on Track. So when you go to a restaurant waiter comes and ask “What would you like to have miss? (With a big smile). We do offer Chinese, continental, Italian” and depending upon your reply “I would like to have Chinese”, Waiter provides you Chinese menu. Is it not simple to understand?  

DEMO

 When to use Factory Pattern?

• ·    When a class does not know which class of objects it must create.
• ·     A class specifies its sub-classes to specify which objects to create.
• ·     In programmer’s language, you can use factory pattern where you have to create an object of any one of sub-classes depending on the data provided.

Advantages of Factory Pattern

·         Factory class removes the dependency on the specific product classes generated by the Factory from the rest of the system. Hence it is based on loose coupling.

·         The system is only dependent on the single interface type that is generated by the Factory.

·         Loosely coupled or decoupled code is easier to test or reuse since the code has fewer  dependencies on other code.

Disadvantages of Factory Pattern

•   If we add any new product (cuisine), we need a new else if statement in GetCuisines method of FactoryDemo class. This violates open/closed design principle.
• We can avoid modifying the Factory class by using sub classing. But sub classing means replacing all the factory class references everywhere through the code.
• We have tight coupling between Factory class and products.

Personal Experience:

When I was in my training period, I was full of confusion. Why should I use a design pattern? I mean what’s the need? Thanks to my mentor who introduced me to the concept of design patterns.

I had to develop PICBUZZ. My life 1^st project that I did sincerely . PICBUZZ is an Artist photo sharing website. All goes well but at last the day came when I had to implement search functionality. Use case was to implement a search functionality on the basis of inputs provided. A user can search a photograph on the basis of Artist name, Album name and Tag name. So I came to know about factory pattern which solved my problem(efficiently) in a second. So this is my short journey of Factory Pattern. Friends I personally believe our experience teaches us many things. So stay connected to my blogs to know more about design patterns.

You can download a sample project from here: https://docs.google.com/file/d/0BzbinC6y3sGqN3dhTEd4c3o5MXc/edit?usp=sharing