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Design Pattern
Milad Abolhassani
tuxgeek.ir milad@tuxgeek.ir
Slides:
http://slideshare.com/miladas http://miladas.github.io/slides
Attention
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Milad Abolhassani tuxgeek.ir milad@tuxgeek.ir Slides: - - PowerPoint PPT Presentation
Milad Abolhassani tuxgeek.ir milad@tuxgeek.ir Slides: - - PowerPoint PPT Presentation
Design Pattern Milad Abolhassani tuxgeek.ir milad@tuxgeek.ir Slides: http://slideshare.com/miladas http://miladas.github.io/slides Attention 2 OOP 3 Class Interface Property Abstract class Method Encapsulation
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OOP
- Class
- Property
- Method
- Inheritance
- Polymorphism
- Interface
- Abstract class
- Encapsulation
- Public/protected/private
- Final
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Where did all of these come from?
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SOLID
SOLID
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SOLID
- Single Responsibility
- Open/Closed
- Liskov substitution
- Interface Segregation
- Dependency Injection
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Single Responsibility
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Open/Closed
- Meyer’s open/closed
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Once class completed, never should modified
- Polymorphic open/closed principle
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Interface (public methods)
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The interface is open for extension but close for modification 8
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Liskov substitution
- Program to an interface rather than of it’s implementation
- Design by contract
- Do not extend the interface
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Interface Segregation
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Dependency injection
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What is design pattern?
- In software engineering, a design pattern is a general reusable
solution to a commonly occurring problem.
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History
- Patterns originated as an architectural concept by Christopher
Alexander (1977/79).
- Design patterns gained popularity in computer science after the book
Design Patterns: Elements of Reusable Object-Oriented Software was published in 1994.
– Gang of Four – Gamma, Erich; Helm, Richard; Johnson, Ralph; Vlissides, John 13
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Gang of four
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Why design pattern?
- Clarity
- Correctness
- Same vocabularies
– Avoid miss communications
- Reuse
- Save time, trial and error
- Can speed up the development process
– by providing tested, proven development paradigms
- We are not reusing code, we are reusing experience
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Category
- Creational design patterns
- Structural design patterns
- Behavioral design patterns
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Creational design patterns
- These design patterns provide a way to create objects while hiding the
creation logic.
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Creational design patterns
- Factory method
- Singleton
- Prototype
- Builder
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Factory Method
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- Factory Method lets a class defer instantiation to
subclasses.
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Singleton
- This pattern involves a single class which is responsible to create an
- bject while making sure that only single object gets created.
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Prototype
- Specify the kinds of objects to create using a prototypical instance, and
create new objects by copying this prototype.
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Builder
- Separate the construction of a complex object from its representation
so that the same construction process can create difgerent representations.
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Programmer
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Structural design patterns
- These design patterns are all about Class and Object composition.
Concept of inheritance is used to compose interfaces and defjne ways to compose objects to obtain new functionalities.
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Structural design patterns
- Adapter
- Decorator
- Facade
- Flyweight
- Proxy
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Adapter
- Convert the interface of a class into another interface clients expect.
Adapter lets classes work together that couldn't otherwise because of incompatible interfaces.
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Decorator
- Attach additional responsibilities to an object dynamically.
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Decorator
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Facade
- Wrap a complicated subsystem with a simpler interface.
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Flyweight
- The Flyweight uses sharing to support large numbers of objects
effjciently.
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Proxy
- Use an extra level of indirection to support distributed, controlled, or
intelligent access.
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Behavioral design patterns
- These design patterns are all about Class's objects communication.
Behavioral patterns are those patterns that are most specifjcally concerned with communication between objects.
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Behavioral design patterns
- Chain of responsibility
- Mediator
- Observer
- State
- Strategy
- Template method
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Chain of responsibility
- The Chain of Responsibility pattern avoids coupling the sender of a
request to the receiver by giving more than one object a chance to handle the request.
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- The Mediator defjnes an object that controls how a set of objects
- interact. Loose coupling between colleague objects is achieved by
having colleagues communicate with the Mediator, rather than with each other.
Mediator
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Observer
- Observer pattern is used when there is one-to-many relationship
between objects such as if one object is modifjed, its depenedent
- bjects are to be notifjed automatically.
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State
- The State pattern allows an object to change its behavior when its
internal state changes.
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Strategy
- In Strategy pattern, a class behavior or its algorithm can be changed at
run time.
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Template method
- The Template Method defjnes a skeleton of an algorithm in an
- peration, and defers some steps to subclasses.
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Thank you
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References
– JavaWorld – SourceMaking – TutorialsPoint – Informit – geekswitblogs – Wikipedia [1] [2]