Design Patterns in Software Engineering

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Introduction to Design Patterns
Author: Kasun Ranga Wijeweera
Email: krw19870829@gmail.com
Date: 2021 March 27
The Design Patterns provide general and reusable solutions to
common problems encountered in software designing.
Design Patterns?
 They are not finished designs those can directly be converted into
programming codes.
 They are not code snippets.
 They are not algorithms.
 They are not components or libraries.
 They are templates to solve problems in Object Oriented Software
Engineering.
 They deal with problems those have already been solved by
someone.
 They can make the process of development faster by providing
tested and proven paradigms.
Origin of Design Patterns
Design Patterns: Elements of Reusable Object-Oriented Software
[Book by Gama, Helm, Johnson, Vlissides (“Gang of Four”, 1994)]

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Four Essential Elements of a Design Pattern
 Name
 Problem
 Solution
 Consequences
Benefits of Design Patterns
 They enhance quality of software design.
 They enable reuse of software architectures extensively.
 They capture expert knowledge explicitly.
 They speed up production in a team.
Drawbacks of Design Patterns
 They do not provide reuse of a direct programming code.
 They are not simple.
 They are validated through experience and discussion rather than
automated testing.
 They may lead teams to suffer from unnecessary overload.
The Three Main Types of Design Patterns
 Creational Design Patterns: Deal with initialization and
configuration of classes and objects.
 Structural Design Patterns: Describe ways of assembling objects to
implement a novel functionality.
 Behavioral Design Patterns: Deal with dynamic interactions among
societies of classes and objects.

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List of Creational Design Patterns
Singleton; Simple Factory; Factory Method; Abstract Factory;
Builder; Prototype; Fluent Interface; Object Pool; Lazy Initialization
List of Structural Design Patterns
Façade; Composite; Flyweight; Proxy; Decorator; Adapter; Bridge
List of Behavioral Design Patterns
Chain of Responsibility; Iterator; Command; Template Method;
Strategy; Observer; Mediator; Memento; State; Interpreter; Visitor