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6. Design: Design Patterns

Choi, Kwanghoon

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Chonnam National University

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Table of Contents

  • Design Pattern

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6.5 Design Patterns

  • A description of problem and the essence of its solution reusable in different settings
  • Design Patterns: Elements of Reusable Object-Oriented Software by GoF (Gang of Four)
    • 23 Design Patterns in 3 types:
      • Creational Pattern types
      • Structural Pattern types
      • Behavioral Pattern types

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http://www.uml.org.cn/c++/pdf/DesignPatterns.pdf

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Design Pattern Types

  • Creational patterns
    • Creation and composition of objects, mechanism to instantiate objects easier, and constraints on the type and number of objects
  • Structural patterns
    • How classes and objects are organized and integrated to build a larger structure
  • Behavioral patterns
    • The assignment of responsibility between objects and the manner in which communication is effected between objects

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23 Design Patterns

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Creational Patterns

Structural Patterns

Behavioral Patterns

  • Abstract Factory
  • Factory method
  • Builder
  • Prototype
  • Singleton
  • Adapter
  • Bridge
  • Composite
  • Decorator
  • Façade
  • Flyweight
  • Proxy
  • Chain of Responsibility
  • Command
  • Interpreter
  • Iterator
  • Mediator
  • Memento
  • Observer
  • State
  • Strategy
  • Template Method
  • Visitor

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Creational Patterns

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  • Abstract factory pattern groups object factories that have a common theme.
  • Factory method pattern creates an object without specifying the exact class to create.
  • Builder pattern constructs complex objects by separating construction and representation.
  • Prototype pattern creates objects by cloning an existing object.
  • Singleton pattern restricts object creation for a class to only one instance.

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Structural Patterns

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  • Adapter pattern allows classes with incompatible interfaces to work together by wrapping its own interface around that of an already existing class.
  • Bridge pattern decouples an abstraction from its implementation so that the two can vary independently.
  • Composite pattern composes zero-or-more similar objects so that they can be manipulated as one object.
  • Decorator pattern dynamically adds/overrides behavior in an existing method of an object.
  • Façade pattern provides a simplified interface to a large bod of code.
  • Flyweight pattern reduces the cost of creating and manipulating a large number of similar objects.
  • Proxy pattern provides a placeholder for another object to control access, reduce cost, and reduce complexity.

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Behavioral Patterns

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  • Chain of Responsibility pattern delegates commands to a chain of processing objects.
  • Command pattern creates objects which encapsulate actions and parameters.
  • Interpreter pattern implements a specialized language.
  • Iterator pattern accesses the elements of an object sequentially without exposing its underlying representation.
  • Mediator pattern allows loose coupling between classes by being the only class that has detailed knowledge of their methods.
  • Memento pattern provides the ability to restore an object to its previous state (undo).
  • Observer pattern is a publish/subscribe pattern which allows a number of observer objects to see an event.
  • State pattern allows an object to alter its behavior when its internal state changes.
  • Strategy pattern allows one of a family of algorithms to be selected on-the-fly at runtime.
  • Template Method pattern defines the skeleton of an algorithm as an abstract class, allowing its subclasses to provide concrete behavior.
  • Visitor pattern separates an algorithm from an object structure by moving the hierarchy of methods into one object.

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Factory Method Pattern

  • Creates an object without specifying the exact class (name) to create

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참고) GoF 디자인 패턴

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Factory Method Pattern

  • Creates an object without specifying the exact class to create

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Example) CreateDocument()

참고) GoF 디자인 패턴

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Application(추상클래스)

CreateDocument()

NewDocument()

PDF Viewer

Picture Viewer

HWP Viewer

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factory method pattern을 사용하도록

리팩토링(refactoring)

참고) Joshua Kerievsky, Refactoring to design patterns

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Abstract Factory Pattern

  • groups object factories that have a common theme

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참고) GoF 디자인 패턴

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Abstract Factory Pattern

  • groups object factories that have a common theme

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참고) 최은만 교재

EIBBulb

EIBBlind

LuxmaterBlind

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Abstract Factory Pattern

  • Q. Draw a class diagram for the following Java programs
    • DesignPatternExamples/src/com/example/designpattern/abstractfactory

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  • Q. Explain the role of FactoryFactory
    • The ElevatorFactoryFactory class

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Singleton Pattern

  • restricts object creation for a class to only one instance.

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public class Singleton {

private static Singleton instance = null;

private Singleton() { … }

public static Singleton getInstance() {

if (instance == null)

instance = new Singleton();

return instance;

}

public void doSomething() {

…

}

}

참고) 정인상, 채흥석, Java로 배우는 디자인패턴

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Adapter Pattern

  • allows classes with incompatible interfaces to work together by wrapping its own interface around a legacy system.

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참고) 최은만 교재

[Problem]

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Adapter Pattern

  • allows classes with incompatible interfaces to work together by wrapping its own interface around a legacy system.

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참고) 최은만 교재

[Solution]

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Adapter Pattern

  • Q. Draw a class diagram for the following Java programs
    • DesignPatternExamples/src/com/example/designpattern/adapter
    • Explain how Client can call specificRequest() in ClassB.

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  • Q. How is it different from the class diagram in the previous slide?
    • Explain each role of the two inheritance relationships in the previous slide. (Target <- Adapter, Adaptee <- Adapter)

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    • Draw a new class diagram for the adapter pattern based on the answer to the second question.

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Composite Pattern

  • composes zero-or-more similar objects so that they can be manipulated as one object.

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참고) GoF 디자인 패턴

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Composite Pattern

  • Draw a class diagram for Computer, ComputerDevice, Client, etc. using this pattern

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참고) 정인상, 채흥석, Java로 배우는 디자인패턴

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Façade Pattern

  • provides a simplified interface to a large body of code.

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참고) 최은만 교재

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Façade Pattern

  • Compiler subsystem classes

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참고) GoF 디자인 패턴

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Façade Pattern

  • Virtual memory framework

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참고) GoF 디자인 패턴

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Iterator Pattern

  • accesses the elements of an object sequentially without exposing its underlying representation.

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  • cf. Iterator, Iterable, for each statement in Java
    • java.lang.Iterator<E>
    • java.util.Iterable<E>

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참고) GoF 디자인 패턴

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Observer Pattern

  • a publish/subscribe pattern which allows a number of observer objects to see an event.

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참고) 최은만 교재

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Observer Pattern

  • a publish/subscribe pattern which allows a number of observer objects to see an event.

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참고) 최은만 교재

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State Pattern

  • allows an object to alter its behavior when its internal state changes (a.k.a. objects for states)

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참고) GoF 디자인 패턴

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State Pattern

  • Light

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OFF

ON

on button

off button

off button

on button

[The initial design]

OFF

ON

on button

off button

off button

on button

[A new design]

SLEEP

on button

off button

참고) 정인상, 채흥석, Java로 배우는 디자인패턴

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State Pattern

  • allows an object to alter its behavior when its internal state changes (a.k.a. objects for states)

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참고) 최은만 교재

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Decorator Pattern

  • dynamically adds/overrides behavior in an existing method of an object.

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Decorator Pattern

  • Various combinations of road displays

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  • new RoadyDisplay().draw()

// 기본 도로 표시

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  • new LaneDecorator(new RoadDisplay()).draw()

// 기본 도로 표시 + 차선 표시

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  • new TrafficDecorator(new RoadDisplay()).draw()

// 기본 도로 표시 + 교통량 표시

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  • new TrafficDecorator(new LaneDecorator(new RoadDisplay())).draw()

// 기본 도로 표시 + 차선 표시 + 교통량 표시

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Decorator Pattern

  • Sequence diagram (roadWithLane.draw)

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참고) GoF 디자인 패턴