Decorator

1
Decorator

• Intent
• Add additional responsibilities and functionality
  to objects dynamically
• Also known as Wrapper
• Example a Text Window

2
Decorator Motivation Application

• Subclassing can only add functionality at runtime
• Avoid enumerating all possible sub classes
• Such as adding a border function to text window.
• Use with optional functionality

3
Decorator Structure

• Participants Component, ConcreteComponent,
  Decorator, ConcreteDecorator

4
Decorator Consequences

• Positives
• More flexibility than static inheritance
• Avoids feature laden classes high in hierarchy
• Negatives
• Lots of little objects
• Interface conformance

5
Flyweight

• Intent Use sharing to support large numbers of
  fine-grained objects efficiently
• Origin
• A boxing class which includes fighters weighing
  less than 112 lb (50 kg) but above 108 lb.
• Example Character in a word processor

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Flyweight Motivation Application

• Applications that could benefit from using
  objects
• But the objects are very small and numerous

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Flyweight Structure

• Participants Flyweight, ConcreteFlyweight,
  UnsharedConcreteFlyweight, FlyweightFactory,
  Client

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Flyweight Consequences

• Positives
• Space saving by using shared objects
• Adds functionality to the application
• Negatives
• Adding processing time of computing extrinsic
  state
• Time can be reduced

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Any Questions?