Builder Pattern

Builder Pattern에 대해 설명하는 페이지입니다.

Posted Dec 24, 2023

By HyunJinNo

Tags

Design Pattern, Java

1. Introduction

• Purpose
  • Allows for the dynamic creation of objects based upon easily interchangeable 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.

2. Characteristics

• 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.
• A Builder is a Strategy that is specialized to create a composite object or data structure
• Builder constructs the object step-by-step and the result is requested at a later stage

3. Participants

• 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

4. How to Use (Example)

• Director

  java

  1public class AerospaceEngineer {
  2    private AirplaneBuilder airplaneBuilder;
  3
  4    public void setAirplaneBuilder(AirplaneBuilder ab) {
  5        airplaneBuilder = ab;
  6    }
  7
  8    public Airplane getAirplane() {
  9        return airplaneBuilder.getAirplane();
  10    }
  11
  12    public void constructAirplane() {
  13        airplaneBuilder.createNewAirplane();
  14        airplaneBuilder.buildWings();
  15        airplaneBuilder.buildPowerplant();
  16        airplaneBuilder.buildAvionics();
  17        airplaneBuilder.buildSeats();
  18    }
  19}

• Abstract Builder

  java

  1public abstract class AirplaneBuilder {
  2    protected Airplane airplane;
  3    protected String customer;
  4    protected String type;
  5
  6    public Airplane getAirplane() {
  7        return airplane;
  8    }
  9
  10    public void createNewAirplane() {
  11        airplane = new Airplane(customer, type);
  12    }
  13
  14    public abstract void buildWings();
  15    public abstract void buildPowerplant();
  16    public abstract void buildAvionics();
  17    public abstract void buildSeats();
  18}

• Product

  java

  1public class Airplain {
  2    private String type;
  3    private float wingspan;
  4    private String powerplant;
  5    private int crewSeats;
  6    private int passengerSeats;
  7    private String avionics;
  8    private String customer;
  9
  10    public Airplain(String customer, String type) {
  11        this.customer = customer;
  12        this.type = type;
  13    }
  14
  15    public void setWingspan(float w) {
  16        this.wingspan = w;
  17    }
  18
  19    public void setPowerplant(String p) {
  20        this.powerplant = p;
  21    }
  22
  23    public void setAvionics(String a) {
  24        this.avionics = a;
  25    }
  26
  27    public void setNumberSeats(int crewSeats, int passengerSeats) {
  28        this.crewSeats = crewSeats;
  29        this.passengerSeats = passengerSeats;
  30    }
  31
  32    public String getCustomer() {
  33        return customer;
  34    }
  35
  36    public String getType() {
  37        return type;
  38    }
  39}

• Concrete Builder

  java

  1public class CropDuster extends AirplaneBuilder {
  2    public CropDuster (String customer) {
  3        super.customer = customer;
  4        super.type = "Crop Duster v3.4";
  5    }
  6
  7    public void buildWings() {
  8        airplane.setWingspan(9f);
  9    }
  10
  11    public void buildPowerplant() {
  12        airplane.setPowerplant("single piston");
  13    }
  14
  15    public void buildAvionics() {}
  16
  17    public void buildSeats() {
  18        airplane.setNumberSeats(1,1);
  19    }
  20}

• Client

  java

  1public class BuilderExample {
  2    public static void main(String[] args) {
  3        // instantiate the director (hire the engineer)
  4        AerospaceEngineeraero = new AerospaceEngineer();
  5
  6        // instantiate each concrete builder (take orders)
  7        AirplaneBuildercrop = new CropDuster("Farmer Joe");
  8        AirplaneBuilderfighter = new FighterJet("The Navy");
  9        AirplaneBuilderglider = new Glider("Tim Rice");
  10
  11        // build a CropDuster
  12        aero.setAirplaneBuilder(crop);
  13        aero.constructAirplane();
  14        Airplane completedCropDuster= aero.getAirplane();
  15        System.out.println(completedCropDuster.getType() +
  16            " is completed and ready for delivery to " +
  17            completedCropDuster.getCustomer());
  18}