Builder Design Pattern - GeeksforGeeks

18 Oct, 2021
Builder pattern aims to “Separate the construction of a complex object from its representation so that the same construction process can create different representations.” It is used to construct a complex object step by step and the final step will return the object. The process of constructing an object should be generic so that it can be used to create different representations of the same object. 
UML Diagram of Builder Design Pattern
 
Source: Wikipedia 
Product – The product class defines the type of the complex object that is to be generated by the builder pattern.
Builder – This abstract base class defines all of the steps that must be taken in order to correctly create a product. Each step is generally abstract as the actual functionality of the builder is carried out in the concrete subclasses. The GetProduct method is used to return the final product. The builder class is often replaced with a simple interface.
ConcreteBuilder – There may be any number of concrete builder classes inheriting from Builder. These classes contain the functionality to create a particular complex product.
Director – The director-class controls the algorithm that generates the final product object. A director object is instantiated and its Construct method is called. The method includes a parameter to capture the specific concrete builder object that is to be used to generate the product. The director then calls methods of the concrete builder in the correct order to generate the product object. On completion of the process, the GetProduct method of the builder object can be used to return the product.
Let’s see an Example of Builder Design Pattern : Consider the construction of a home. Home is the final end product (object) that is to be returned as the output of the construction process. It will have many steps like basement construction, wall construction, and so on roof construction. Finally, the whole home object is returned. Here using the same process you can build houses with different properties. 
Java
interface HousePlan{    public void setBasement(String basement);     public void setStructure(String structure);     public void setRoof(String roof);     public void setInterior(String interior);} class House implements HousePlan{     private String basement;    private String structure;    private String roof;    private String interior;     public void setBasement(String basement)    {        this.basement = basement;    }     public void setStructure(String structure)    {        this.structure = structure;    }     public void setRoof(String roof)    {        this.roof = roof;    }     public void setInterior(String interior)    {        this.interior = interior;    } }  interface HouseBuilder{     public void buildBasement();     public void buildStructure();     public void buildRoof();     public void buildInterior();     public House getHouse();} class IglooHouseBuilder implements HouseBuilder{    private House house;     public IglooHouseBuilder()    {        this.house = new House();    }     public void buildBasement()    {        house.setBasement("Ice Bars");    }     public void buildStructure()    {        house.setStructure("Ice Blocks");    }     public void buildInterior()    {        house.setInterior("Ice Carvings");    }     public void buildRoof()    {        house.setRoof("Ice Dome");    }     public House getHouse()    {        return this.house;    }} class TipiHouseBuilder implements HouseBuilder{    private House house;     public TipiHouseBuilder()    {        this.house = new House();    }     public void buildBasement()    {        house.setBasement("Wooden Poles");    }     public void buildStructure()    {        house.setStructure("Wood and Ice");    }     public void buildInterior()    {        house.setInterior("Fire Wood");    }     public void buildRoof()    {        house.setRoof("Wood, caribou and seal skins");    }     public House getHouse()    {        return this.house;    } } class CivilEngineer{     private HouseBuilder houseBuilder;     public CivilEngineer(HouseBuilder houseBuilder)    {        this.houseBuilder = houseBuilder;    }     public House getHouse()    {        return this.houseBuilder.getHouse();    }     public void constructHouse()    {        this.houseBuilder.buildBasement();        this.houseBuilder.buildStructure();        this.houseBuilder.buildRoof();        this.houseBuilder.buildInterior();    }} class Builder{    public static void main(String[] args)    {        HouseBuilder iglooBuilder = new IglooHouseBuilder();        CivilEngineer engineer = new CivilEngineer(iglooBuilder);         engineer.constructHouse();         House house = engineer.getHouse();         System.out.println("Builder constructed: "+ house);    }}
Output :  
Builder constructed: House@6d06d69c
Advantages of Builder Design Pattern
The parameters to the constructor are reduced and are provided in highly readable method calls.
Builder design pattern also helps in minimizing the number of parameters in the constructor and thus there is no need to pass in null for optional parameters to the constructor.
Object is always instantiated in a complete state
Immutable objects can be built without much complex logic in the object building process.
 Disadvantages of Builder Design Pattern
The number of lines of code increases at least to double in builder pattern, but the effort pays off in terms of design flexibility and much more readable code.
Requires creating a separate ConcreteBuilder for each different type of Product.
Further Read: Builder Method in Python.This article is contributed by Saket Kumar. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. 
swyrik
Pushpender007
Design Pattern
Writing code in comment?
Please use ide.geeksforgeeks.org,
generate link and share the link here.
Comments
Old Comments
SDE SHEET - A Complete Guide for SDE Preparation
Factory method design pattern in Java
Unified Modeling Language (UML) | An Introduction
Introduction of Programming Paradigms
MVC Design Pattern
Unified Modeling Language (UML) | State Diagrams
Unified Modeling Language (UML) | Activity Diagrams
How to design a parking lot using object-oriented principles?
Monolithic vs Microservices architecture
Unified Modeling Language (UML) | Class Diagrams