Design Patterns - 01 Introduction and Decorator Pattern
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01 Introduction & Decorator Pattern Design Patterns © Prafulla Paraskar 2010
Transcript of Design Patterns - 01 Introduction and Decorator Pattern
© Prafulla Paraskar 2010
01 Introduction & Decorator Pattern
Design Patterns
Introduction
DESIGN PATTERNS - DEFINITION Definition:
a general reusable solution to a commonly occurring problem in software design (Wikipedia).
Not a finished design Description or template for how to solve a
problem that can be used in many different situations
Shows relationships and interactions between classes and/or objects
Not all software patterns are design patterns (e.g. algorithms)
DESIGN PATTERNS – CLASSIFICATION
Structural Pattern Ease the design by identifying a simple way to realize
relationships between entities E.g. Decorator, Proxy
Creational Pattern Deal with object creation mechanism E.g. Abstract Factory, Singleton
Behavioral Pattern Deal with common communication between objects. E.g. Chain of Responsibility, Command
Concurrency Pattern Deal with multi-threaded programming paradigm. E.g. Monitor Object, Thread Pool Not covered during this series
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DESIGN PATTERNS – CLASSIFICATIONStructural Patterns
• 1. Decorator• 2. Proxy• 3. Bridge• 4. Composite• 5. Flyweight• 6. Adapter• 7. Facade
Creational Patterns• 1. Prototype• 2. Factory Method• 3. Singleton• 4. Abstract
Factory• 5. Builder
Behavioral Patterns• 1. Strategy• 2. State• 3.
TemplateMethod• 4. Chain of
Responsibility• 5. Command• 6. Iterator• 7. Mediator• 8. Observer• 9. Visitor• 10. Interpreter• 11. Memento
UML CLASS DIAGRAM NOTATION (1/3)
UML CLASS DIAGRAM NOTATION (2/3)
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UML CLASS DIAGRAM NOTATION (3/3)
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DecoratorStructural Design Pattern
DEFINITION
In object-oriented programming, the decorator pattern is a design pattern that allows new/additional behaviour to be added to an existing object dynamically.
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DECORATOR PATTERN – EXPLAINED (1/2)
Photo+
Frame+
CaptionGuptas (2010)
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DECORATOR PATTERN – EXPLAINED (2/2) Adds functionality at Runtime.
The object does not know it is being “decorated”.
Three is no one big feature-laden class with all the options in it.
The decorations are independent of each other.
The decorations can be composed together in a mix-and-match fashion.
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DECORATOR PATTERN – UML DIAGRAM
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DECORATOR PATTERN – REAL WORLD SAMPLES Graphics world (as illustrated). I/O namespace of .NET
System.IO.Stream System.IO.BufferedStream System.IO.FileStream System.IO.MemoryStream
Cross platform applications (Mobile/Desktop) Actual decorator classes in .NET 3.0
System.Windows.Controls (Base Class) Border (Decorator) Viewbox (Decorator)
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DECORATOR PATTERN – GUIDELINES (1/2) You have:
An existing component class that may be unavailable for subclassing.
You want to: Attach additional state or behavior to an object
dynamically. Make Changes to some objects of a class without affecting
others. Avoid subclassing because too many classes could result.
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But consider using instead: The Adapter Pattern
Sets up an interface between different classes The Composite Pattern
Aggregates an object without also inheriting its interface. The Proxy Pattern
Specifically controls access to objects. The Strategy Pattern
Changes the original object rather than wrapping it.
DECORATOR PATTERN – GUIDELINES (2/2)
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