Design patterns why we need them? What are there uses? Essential elements and GoF!

1. Name: Zubair Ahmed
Roll No: K19SW01
Department: Software Engineering
Subject: Software Design and Architecture
Uni: MUET SZAB Khairpur Mir’s
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2. Design Patterns
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3. Table of Contents
 Design Patterns
 Why Design Patterns
 Design Pattern: Usage
 The Concept OF Patterns Construction Architecture Patterns
 Design Pattern: Essential Elements
 GoF Design Patterns
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4. Design Patterns
1. It describes a general usable solution to a recurring problem in an environment
2. It describes core of solution in a procedural-like structure
3. It isn’t a finished design that can be transformed directly into code, but a description or
template for how to solve a problem that can be used in many different situations
4. Design patterns are “descriptions of communicating objects and classes that are
customized to solve a general design problem in a particular context.”
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5. Why Design Patterns?
1. Simplifies object identification
2. Simplifies system decomposition
3. Proven & tested technique for problem solving
4. Improves speed & quality of design / implementation
5. Can be adapted / refined for specific system under construction.
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6. Design Patterns: Usage
Design patterns:
• Provide general solutions, documented in a format that doesn’t require specifics tied to a
particular problem
• Can speed up the development process by providing tested, proven development
paradigms
• Help you benefit from the experience of fellow developers
• Prevent subtle issues that can cause major problems
• Improve code readability for coders and architects familiar with them
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7. THE CONCEPT OF PATTERNS Construction Architecture
Patterns
 The first idea of using patterns was for building and proposed by the architect Christopher
Alexander.
 He found recurring themes in architecture, and captured them into descriptions
 He called them patterns.
 The term 'pattern' appeals to the replicated similarity in a design
 The similarity makes room for variability and customization in each of the elements
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8. Cont…
 Alexander defines: «Each pattern is a three part rule which express a relation between a
certain context, a problem and a solution.
 Each pattern is a relationship between
 A certain context,
 A certain system of forces which occurs repeatedly in that context
 A certain spatial configuration which allows these forces to resolve themselves.
 A pattern is an instruction and shows how this configuration can be used over and over
again.
 The pattern is a thing that happens in the world
 The rule which tell us how to create that thing and when we must create it.
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9. Design Patterns: Essential Elements
 A pattern has four essential elements:
 The pattern name that we use to describe a design problem
 The problem that describes when to apply the pattern
 The solution that describes the elements that make up the design
 The consequences that are the results and trade-offs of applying the pattern
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10. GoF Design Patterns
 The Gang of Four are the four authors of the book « Design Patterns: Elements of
Reusable Object-Oriented Software »
 Defined 23 design patterns for recurrent design issues, called GoF design patterns
 Classified by purpose:
 Structural : Concerns the composition of classes and objects
 Behavioral : Characterizes the interaction and responsibility of objects and classes
 Creational : Concerns the creation process of objects and classes
 … and by scope:
 Class scope: relationship between classes and subclasses, defined statically
 Object scope: object relationships, dynamic
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