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Design Patterns

Learn recurring solutions to programming challenges, isolated code changes, and object interactions using design patterns. Examples include Facade, Adapter, Singleton, Abstract Factory, and Bridge.

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Design Patterns

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  1. Design Patterns By Mareck Kortylevitch and Piotreck Ratchinsky

  2. What is Design Pattern? • Recurring solution to known problems • Workaround to problems that arise when developing software within a particular context

  3. History • Precursor of design pattern was Christopher Alexander • First Design Patterns used in architecture

  4. Why to use DP? • Help you learn from others' successes instead of your own failures • Provide a communication platform concerning elegant, reusable solutions to commonly encountered programming challenges

  5. Why to use...continuation • Enforce using techspeak • Isolate changes in the code • Design and interaction of objects

  6. Design Patterns Examples • Facade • Adapter • Singleton • Abstract Factory • Bridge

  7. Facade - definition • Provide a unified interface to a set of interfaces in a subsystem. Façade defines a higher-level interface that makes the subsystem easier to use.

  8. Facade - UML class diagram

  9. Facade - example • Facade (MortgageApplication) • knows which subsystem classes are responsible for a request. • delegates client requests to appropriate subsystem objects. • Subsystem classes (Bank, Credit, Loan) • implement subsystem functionality. • handle work assigned by the Facade object. • have no knowledge of the facade and keep no reference to it.

  10. Facade – example diagram Facade Subsystems Bank Credit Loan

  11. Singleton - definition • ensure a class has only one instance and provide a global point of access to it. • defines an Instance operation that lets clients access its unique instance. Instance() is a class operation. • responsible for creating and maintaining its own unique instance.

  12. Singleton – UML Singleton -static Singleton: instance -Singleton() +static getInstance():Singleton

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