Short Notes: Design Principles & Patterns

History

The book called “A Pattern Language”[1]  by C.Alexander is the fundamental reference for the book named “Design Patterns (GoF)”, which is generally accepted as the standard in building software.

[1] https://en.wikipedia.org/wiki/A_Pattern_Language

A pattern language [2] is a method of describing good design practices or patterns of useful organization within a field of expertise.

[2] https://en.wikipedia.org/wiki/Pattern_language

Architectural Concepts

Envision - Examine stakeholder goals combined with architect’s expertise.
Model - View the ‘lay of the land’ to construct a model  and set expectations.
Blueprint - Specify the construction details  and constraints.
Inspect - Verify construction implementation.
Term Nomenclature - communicate  in terms understandable to listeners.

Mapping to software field

Envision - Software Architecture
Model - Design Patterns
Blueprint - Construction & Design principles 
Inspect - Construction patterns
Nomenclature - Terms to communicate intent


Software Architecture

Web server - A pipeline architecture
SOA - A component architecture
Client/Server - A layered architecture
Single Tier - Monolithic Architecture
Cloud - A tier network architecture

Design Patterns

Creational
Structural & Behavioral
Event Driven
Plugins

Design Principles

Abstraction
Encapsulation
Cohesion
Coupling
Complexity

Construction Patterns

Inheritance Design
Component Design
Layered Design
Tier Design
Delivery methodology
Software Architecture erosion (“Decay”)

OO Basics

Abstraction
Encapsulation
Polymorphism
Inheritance

OO Principles

• Encapsulate what varies - Identify different behaviors
• Favor composition over inheritance
• Program to interfaces, not implementation
• Strive for loosely coupled designs between objects that interact.
• Open Close : Class should be open for extension but close for modification.
• Dependency Inversion : Depend upon abstraction. Do not depend upon concrete classes.
• Least Knowledge : Talk only to your immediate friends.

OO Patterns

What is a pattern : A reusable solution to a problem which occurring in a particular context.

Structure of a pattern

Name
Context - situation
Problem
Forces
Solution
Resulting Contex -  1. Benefits 2. Drawbacks 3. Issues to resolve
Related Patterns

Three fundamental groups

https://www.gofpatterns.com/design-patterns/module2/three-types-design-patterns.php


Behavioral patterns - Describe interactions between objects

• Command - https://www.tutorialspoint.com/design_pattern/command_pattern.htm

• Observer - https://www.tutorialspoint.com/design_pattern/observer_pattern.htm

• Strategy - https://www.tutorialspoint.com/design_pattern/strategy_pattern.htm

• Template pattern - https://www.tutorialspoint.com/design_pattern/template_pattern.htm

• Interpreter pattern -

Creational- Make objects of the right class for a problem

• Factory - https://www.journaldev.com/1392/factory-design-pattern-in-java

• Abstract Factory - https://www.journaldev.com/1418/abstract-factory-design-pattern-in-java

• Factory vs Abstract Factory

• Singleton-

Structural- Form larger structures from individual parts, generally of different classes.

• Decorator - https://www.tutorialspoint.com/design_pattern/decorator_pattern.htm

• Facade (Unified Interface)- https://www.tutorialspoint.com/design_pattern/facade_pattern.htm

• Addapter - https://www.tutorialspoint.com/design_pattern/adapter_pattern.htm