Flyweight Design Pattern

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Flyweight Design Pattern
Adwoa Donyina Chaitanya Bhatt
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Overview

• Structural Design Patterns
• FlyWeight
• Example and Exercise 1 and 2
• Related Pattern State Pattern
• Example

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Structural Patterns

• Composition of Classes and Objects to form larger
  structures.
• Structural Class Patterns
• Use of Inheritance to compose interfaces or
  implementations.
• Structural Object Patterns
• Different ways to compose objects to realize new
  functionality.

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Structural Patterns

• Class Patterns
• Adapter

• Object Patterns
• Composite
• Proxy
• Flyweight
• Façade
• Decorator
• Bridge

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Flyweight Design Pattern

• A shared object that can be used in multiple
  contexts.
• Applicability
• Lots of Objects
• Most Objects can be made extrinsic.
• Have pools of objects with common states
• Objects Identity is not important

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Flyweight Design Pattern
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Flyweight Design Pattern

• Intrinsic V.S. Extrinsic
• Intrinsic is stored in the flyweight it stores
  information that is independent of the context so
  its sharable.
• Extrinsic Depends on and varies with the
  context. Client passes in the extrinsic state.

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Flyweight Design Pattern

• Concrete Flyweight
• Sharable
• Stored states are intrinsic
• Unshared Concrete Flyweight
• Not Sharable
• Stored states are context driven

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Flyweight Design Pattern

• Consequences
• Flyweights introduce run-time costs associated
  with transferring, finding, and/or computing
  extrinsic state Costs are offset by space savings
  and depend on
• Reduction in the total of objects
• Amount of intrinsic state per object
• Whether extrinsic state is computed or stored
• Often State Pattern is implemented as Flyweights

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Flyweight Design Pattern

• Example
• Exercise 1
• Map the flight path!!! Ok that doesnt make
  sense.
• Exercise 2

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Behavioral Patterns

• To help define assignment of responsibilities
  between objects.
• Communication between Classes and Objects
• Eg. State design pattern

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State Design Pattern

• Allow an object to alter its behavior when its
  internal state changes.
• The object will appear to change its class.

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Flyweight Design Pattern
Example 2