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I presented my understanding on few design patterns to my team @ex employer. They liked it coz of its simplicity and crips and clear.
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Design Patterns
Shailesh Kumar S
Agenda
Structural Design Patterns:AdapterDecoratorBridgeFacade
Structural Patterns What?
Defines composition between entities to build larger systems.
Why? Helps in understanding the relationship between
classes and objects.
How? By using following Patterns:
Adapter, Facade, Bridge, Decorator, etc.
Adapter Pattern What?
Translate one interface of a class into a compatible interface.
Why? And old legacy class needs to be reused, but its
interface is different than application expects.
Example 1:
Example 2:
Decorator Pattern What?
Defines attaching new responsibility to the object dynamically.
Why? Helps in wrapping an existing object with another
object with out breaking the interface or other objects.
Example 1:
Example 2:
Bridge Pattern What?
Separates objects interface and its implementation.
Why? Both abstraction and implementation can vary
independently. Avoiding hard binding between abstraction and
implementation. Reduce number of sub classes and this reduction
in code size.
Example: House electrical equipment and switch Text file storage and representation across
operating systems.
Facade Pattern
What? An Higher level interface to a complex sub-
system to simplify communication.
Why? Re-structuring a complex system into less
complex sub-systems
Reduce dependencies between sub-systems.
Example:
Client Object 1 Client Object 2
Client objects
Sub-systems objects
Ordering System
Billing System
Query System
Client Object 3
With Facade Pattern:
Example:
Customer Service Support system
Library Management system
Client objects
Sub-system objects
Facade
Client Object 2Client Object 1
Client Object 3
Billing System
Ordering System
When to choose what:Adapter: You want to use an existing class, and its interface does not
match the one you need.
Decorator: When you want to enhance the responsibilities of an object.
When extension for an object via sub-classing is complex/tedious.
Bridge: Only applied before the classes are designed.
When both side of the interfaces can vary independently.
Facade:
When you want to define new interface for a group of objects with out adding new functionality.
When you want to represent 1 object for a group of objects to simplify communication.
Questions?
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