Design Patterns
What are design patterns?
A general reusable solution to a commonly
occurring problem.
A description or template for how to solve
a problem that can be used in many
different situations.
For example…
Gang of Four
Words to live by
Program to an interface, not an implementation.
Favor object composition over class inheritance.
Interfaces: good
Inheritance: bad
Types of design patterns
• Creational
– Instantiation of objects
• Structural
– Class and object composition
• Behavioral
– Communication between objects
Creational patterns
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Abstract Factory
Builder
Factory Method
Prototype
Singleton
Creational patterns
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Abstract Factory
Builder
Factory Method
Prototype
Singleton
Structural patterns
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Adapter
Bridge
Composite
Decorator
Façade
Flyweight
Proxy
Structural patterns
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Adapter
Bridge
Composite
Decorator
Façade
Flyweight
Proxy
Behavioral patterns
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Chain of responsibility
Command
Interpreter
Iterator
Mediator
Memento
Observer
State
• Strategy
• Template method
• Visitor
Behavioral patterns
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Chain of responsibility
Command
Interpreter
Iterator
Mediator
Memento
Observer
State
• Strategy
• Template method
• Visitor
And this affects me how?
• What are design patterns used for?
• What are the three categories of GoF
design patterns?
• Patterns you should be able to describe
– Singleton
– Composite
– Façade
– Chain-of-responsibility
– Observer