Design Patterns
Preparer: Chip Salim
Thursday, April 7 2017
Preface
- Re-fresher & Discovery
- Change always happens
- Increase communication
- Thinking in patterns
Driving Factors:
Foundation
A Pie
- Abstraction
- Polymorphism
- Inheritance
- Encapsulation
OO Basics
Foundation
OO Principles
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A class should only have 1 reason to change (Single Responsibility Principle)
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Don't repeat the same code (DRY Principle)
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Depend on abstraction not on concrete classes (Dependency Injection Principle)
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Favor composition over inheritance
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Encapsulate what varies (Interface Segregation Principle)
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Don't call us, we'll call you (Hollywood Principle)
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Classes should be open for extension but closed for modification (Open Closed Principle)
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Only talk to your friends
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Program to interfaces, not implementation (Liskov Substitution Principle)
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Strive for loosely coupled designs between objects that interact
Design Patterns are and are not
- DP are created from discoveries of recurring problems
- DP are best practices formulated to overcome such problems
- DP are general design solutions to resolve any constraints when achieving your coding goals
- DP is art
- DP is tools
- DP adds efficiency
- DP are not coding solutions but guidelines
- DP are not meant to add complexity
- DP are not always immediately obvious
When to use and when not to use DP
- KISS first
- Think over and decide the trade-off
- Address issues of change in software
- Size doesn't matter.
- Based on experience and knowledge
- A hunch
- Refactor
Let a DP emerge from your designs
Make DP one of the options in the design
When to use DP
- Refactoring time
- Based on experience and knowledge
- DP are not coding solutions but guidelines
- DP are not meant to add complexity
- DP are not always obvious
How to use DP
- Use Class Diagram
- Use DP Catalog
- Must posses strong OOB
- Must understand the underlying OOP
- Talk to your peers
- OK to alter
Benefit
- Increase Communication
- Building flexible, reusable, maintanable apps
- Reduce or even eliminate complexity from existing codes
- Refactor - Often introduce more layers.
Trade Off
DP Types
Behavioral
Creational
Structural
Conccurency
Design Patterns Catalog
dofactory.com
sourcemaking.com
Strategy Pattern
Thank You Por Favor
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Design Patterns feat. Strategy Pattern
By ilusi
