Design Patterns: A Comprehensive Overview
Design Patterns
Rashed Fatehi
Introduction
Introduction
•
OOP?
•
Resolve complexity?
•
Why design patterns?
What is design pattern?
What is design pattern?
Design patterns
are typical solutions to common problems in software
design.
The Catalog of Design Patterns
1.
Singelton
2.
Factory Method
3.
Abstract Factory
4.
Builder
5.
Prototype
1.
Adapter
2.
Facade
3.
Decorator (Wrapper class)
4.
Proxy
5.
Flyweight
1.
Chain of responsibility
2.
Mediator
3.
Observer
4.
Proxy
5.
Strategy
6.
Template method
Let’s talk about design patterns in
action
Strategy pattern
Strategy pattern
interface IStrategy is
method execute(a, b)
class ConcreteStrategyAdd implements IStrategy is
method execute(a, b) is
return a+b
class ConcreteStrategySubtract implements IStrategy is
method execute(a, b) is
return a-b
class context is
Strategy: IStrategy;
method executeStrategy(int a, int b) is
return strategy.execute(a, b)
Strategy pattern
class ExampleApplication is
method main() is
Create context object.
Read first number.
Read last number.
Read the desired action from user input.
if (action == addition) then
context.setStrategy(new ConcreteStrategyAdd())
if (action == subtraction) then
context.setStrategy(new ConcreteStrategySubtract())
result = context.executeStrategy(First number, Second number)
Print result
Decorator pattern (Wrapper class)
Decorator pattern (Wrapper class)
class OddOrEvenDecorator implements IStrategy is
Private _strategy: IStrategy;
method executeStrategy(int a, int b) is
return strategy.execute(a, b)
method IsEven(int a) is
return a % 2 == 0;
method IsOdd(int a) is
return a % 2 != 0;
Decorator pattern (Wrapper class)
class ExampleApplication is
method main() is
Create context object.
Read first number.
Read last number.
Read the desired action from user input.
if (action == addition) then
context.setStrategy(new OddOrEvenDecorator (new ConcreteStrategyAdd()))
if (action == subtraction) then
context.setStrategy(new OddOrEvenDecorator (new ConcreteStrategySubtract()))
result = context. Strategy.IsOdd(First number)
Print result
Facade pattern
Factory method pattern
Factory method pattern
abstract class AbstractDialog is
abstract method createButton():Button
method render() is
Button okButton = createButton()
okButton.render()
class WindowsDialog extends AbstractDialog is
method createButton():Button is
return new WindowsButton()
class WebDialog extends AbstractDialog is
method createButton():Button is
return new HTMLButton()
Factory method pattern
class Application is
field dialog: AbstractDialog
method initialize() is
config = readApplicationConfigFile()
if (config.OS == "Windows") then
dialog = new WindowsDialog()
else if (config.OS == "Web") then
dialog = new WebDialog()
else
throw new Exception("Error! Unknown operating system.")method main() is
this.initialize()
dialog.render()
Singelton pattern
Singelton pattern
Class Database is
private static field instance: Database
private constructor Database() is
//Some Initiolization code
public static method getInstance() is
if (Database.instance == null) then
acquireThreadLock() and then
if (Database.instance == null) then
Database.instance = new Database()
return Database.instance
Chain of responsibility pattern
Observer pattern
Refrences
•
Why is OOP Such a Waste?. A waste of time of money. | by Ilya Suzdalnitskiy |
Medium
•
Design Patterns (refactoring.guru)
•
Author, Eric Freeman & Author, Elisabeth Robson & Author, Bert Bates &
Author Kathy Sierra (2004).Head First Design Patterns. Location: O'Reilly
Exploring the world of design patterns, this content delves into the essence of design patterns, their application in software design to resolve complexity, and the different types of design patterns - creational, structural, and behavioral. It also showcases examples of popular design patterns such as Strategy and Decorator, providing detailed insights into their implementation and usage in real-world scenarios.
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Presentation Transcript
Design Patterns Rashed Fatehi
Introduction OOP? Resolve complexity? Why design patterns?
What is design pattern? Design patterns are typical solutions to common problems in software design.
The Catalog of Design Patterns Singelton Factory Method Abstract Factory Builder Prototype 1. Creational patterns: Provide various object creation mechanisms 2. 3. 4. 5. Adapter Facade Decorator (Wrapper class) Proxy Flyweight 1. Structural patterns: Explain how to assemble objects and classes into larger structures, while keeping these structures flexible and efficient 2. 3. 4. 5. Chain of responsibility Mediator Observer Proxy Strategy Template method 1. Behavioral patterns: Concerned with algorithms and the assignment of responsibilities between objects 2. 3. 4. 5. 6.
Strategy pattern interface IStrategy is method execute(a, b) class ConcreteStrategyAdd implements IStrategy is method execute(a, b) is return a+b class ConcreteStrategySubtract implements IStrategy is method execute(a, b) is return a-b class context is Strategy: IStrategy; method executeStrategy(int a, int b) is return strategy.execute(a, b)
Strategy pattern class ExampleApplication is method main() is Create context object. Read first number. Read last number. Read the desired action from user input. if (action == addition) then context.setStrategy(new ConcreteStrategyAdd()) if (action == subtraction) then context.setStrategy(new ConcreteStrategySubtract()) result = context.executeStrategy(First number, Second number) Print result
Decorator pattern (Wrapper class) class OddOrEvenDecorator implements IStrategy is Private _strategy: IStrategy; method executeStrategy(int a, int b) is return strategy.execute(a, b) method IsEven(int a) is return a % 2 == 0; method IsOdd(int a) is return a % 2 != 0;
Decorator pattern (Wrapper class) class ExampleApplication is method main() is Create context object. Read first number. Read last number. Read the desired action from user input. if (action == addition) then context.setStrategy(new OddOrEvenDecorator (new ConcreteStrategyAdd())) if (action == subtraction) then context.setStrategy(new OddOrEvenDecorator (new ConcreteStrategySubtract())) result = context. Strategy.IsOdd(First number) Print result
Factory method pattern abstract class AbstractDialog is abstract method createButton():Button method render() is Button okButton = createButton() okButton.render() class WindowsDialog extends AbstractDialog is method createButton():Button is return new WindowsButton() class WebDialog extends AbstractDialog is method createButton():Button is return new HTMLButton()
Factory method pattern class Application is field dialog: AbstractDialog method initialize() is config = readApplicationConfigFile() if (config.OS == "Windows") then dialog = new WindowsDialog() else if (config.OS == "Web") then dialog = new WebDialog() else throw new Exception("Error! Unknown operating system.") method main() is this.initialize() dialog.render()
Singelton pattern Class Database is private static field instance: Database private constructor Database() is //Some Initiolization code public static method getInstance() is if (Database.instance == null) then acquireThreadLock() and then if (Database.instance == null) then Database.instance = new Database() return Database.instance
Refrences Why is OOP Such a Waste?. A waste of time of money. | by Ilya Suzdalnitskiy | Medium Design Patterns (refactoring.guru) Author, Eric Freeman & Author, Elisabeth Robson & Author, Bert Bates & Author Kathy Sierra (2004).Head First Design Patterns. Location: O'Reilly
