[Design Pattern] Builder Pattern (빌더 패턴)

Builder Pattern

Builder Pattern 중 Director와 Builder의 관계는 전략 패턴은 생성에 적용한 패턴이라고도 할 수 있다. 즉, 다양한 생성 알고리즘을 구현하는 ConcreteBuilder는 그 구현체 수 만큼 다양한 Product을 반환한다. Client는 최종적으로 반환하는 Product을 조금 더 유연하게 생성하기 위해 Builder Pattern을 적용한다.

• Purpose
  • Allows for the dynamic creation of objects based upon easily interchageable algorithms
• Use When
  • Runtime control over the creation process is required
  • Multiple representations of creation algorithms are required
  • Object creation algorithms should be decoupled from the system
  • The addition of new creation functionality without changing the core code is necessary
• Comparison with Abstract Factory
  • Builder constructs the object step-by-step and the result is requested at a later stage
  • Builder Pattern focuses only the result object
  • Abstract factory returns the requetsted object immediately
  • Abstract factory does not have an abstract builder; application calls the factory method directly

Builder Pattern Structure

• Director knows what parts are needed for the final product
• Concrete builder knows how to produce the part and add it to the final product

• Client
  • selects director and concrete builder to build the product
  • asks concrete builder to return final constructed product
• Director
  • knows what steps it takes to build a product
  • but it does not know how each step is to be carried out
• Builder
  • specifies an abstract interface for creating parts of a Product object
• Concrete Builder
  • constructs and assembles parts of the product by implementing the Builder interface
  • defines and keeps track of the representation it creates
  • provides an interface for retrieving the product
• Product
  • represents the complex object under construction

When a Builder Shouldn’t be Used

• If the interface is not stable the Builder has few benefits
  • Every interface change requires a change to the Controller and impacts the abstract base class or its objects
  • A new method would require changing the base class and all concrete classes that will need to override the new method
  • A specific method interface change would require all concrete classes supporting the old method to change