We'll discuss the concept of the Design Pattern in this session. A basic go through of: * What are Design Patterns? * Why we should know Design Patterns? * How to use Design Patterns? With a Demonstration of some of its types.

1. Design Patterns
By :-
Yashpal
Sr. Software Consultant
KNOLDUS Inc.

2. The Agenda
● What, What not?
● Why?
● How?
○ Classification and when to use what?
○ Demo

3. What, What not?
The principle states that we should always prefer
Composition over Inheritance, and code for
interface not for Implementation.
Design Patterns:
● Are reusable solutions to the commonly
occurring problem within a given context in
software design.
● Aren’t finished design that can be transformed
directly into code

4. Why?
● Design patterns can speed up the
development process by providing
tested, proven development paradigms.
● Helps to prevent invisible issues prior
to development.
● Improves code readability.

5. How?
Classification
Creational
➔ Singleton
➔ Factory
➔ Abstract Factory
➔ Builder
➔ Prototype
Structural
➔ Adapter
➔ Composite
➔ Proxy
➔ Fly Weight
➔ Facade
➔ Bridge
➔ Decorator
Behavioral
➔ Template Method
➔ Mediator
➔ Chain
➔ Chain of Responsibility
➔ Observer
➔ Strategy
➔ Command
➔ State
➔ Visitor
➔ Iterator
➔ Interpreter
➔ Memento

6. How?
Classification: Creational
When we want to create an object then we should use Creational Design
Patterns.
➔ Singleton
➔ Factory
➔ Abstract Factory
➔ Builder
➔ Prototype

7. How?
Creational: Factory Pattern
A Pattern which manufactures Objects for you on demand without making
changes to your client application, keeping real objects abstracted.

8. How?
Creational: Builder Pattern
➔ Used to build complex Objects using simpler objects with a step by step
approach.

9. How?
Creational: Prototype Pattern
➔ Involves creating objects by cloning them from existing ones. Its purpose is
related to performance and keeping it high by trying to avoid expensive calls.

10. How?
Classification: Structural
When we want to Compose Objects then we should use Structural Design Patterns.
➔ Adapter
➔ Composite
➔ Proxy
➔ Fly Weight
➔ Facade
➔ Bridge
➔ Decorator

11. How?
Structural: Adapter Pattern
➔ Involves creating objects which are compatible with target system by
implementing the incompatible client and using the target system instance in
an Adapter Class.

12. How?
Structural: Composite Pattern
➔ When you need to create an object which represents a tree structure.

13. How?
Classification: Behavioral
When we want objects to communicate without composing them then we should Behavioral Design
Patterns.
➔ Template Method
➔ Mediator
➔ Chain
➔ Chain of Responsibility
➔ Observer
➔ Strategy
➔ Command
➔ State
➔ Visitor
➔ Iterator
➔ Interpreter
➔ Memento

14. References
Design Patterns Wikipedia