Aayush Tuladhar

Design Patterns - The Builder Pattern

21 Dec 2016

Builder Pic

Intent

  • Separate the Construction of Complex Object from it’s representation
  • Facilitate building complex objects where multiple parameters are involved.

Problem

  • Encapsulate the construction and assembling of complex object in separate Builder Object.
  • Inflexibility with Constructors to create complex objects.

Solution

It provides static factory builder object to start and facilitates adding additional parameters.

Summary

  • Builder Design Pattern falls under Creational Pattern which facilitates flexibility and readability while creating multiple objects because same builder can be re-used.

Builder Pattern

Example

UserTest.java

package com.art.designpatterns.builder;

import lombok.Getter;
import lombok.Setter;
import lombok.ToString;

@Getter
@Setter
@ToString
class User {
    private String firstName;
    private String lastName;
    private String email;
    private String address;
}

/**
 * Demo Class
 */
class UserBuilderTest{
  public static void main(String[] args) {
    User johnDoe = new UserBuilder("John", "Doe").build();
    User robertNoyce = new UserBuilder("Robert", "Noyce")
                                .email("robert.noyce@gmail.com")
                                .address("Burlington, IA").build();
    System.out.println(johnDoe);
    System.out.println(robertNoyce);
  }
}

UserBuilder.java

package com.art.designpatterns.builder;

public class UserBuilder {

  private User user;

  //Required
  private String firstName;
  private String lastName;

  //Defaults
  private String email = "";
  private String address = "";

  /**
   * UserBuilder with firstName and lastName as required Parameters
   * @param firstName
   * @param lastName
   */
  public UserBuilder(String firstName, String lastName){
    this.firstName = firstName;
    this.lastName = lastName;
  }

  public UserBuilder email(String email){
    this.email = email;
    return this;
  }

  public UserBuilder address(String address){
    this.address = address;
    return this;
  }

  public User build(){
    user = new User();
    user.setFirstName(firstName);
    user.setLastName(lastName);
    user.setEmail(email);
    user.setAddress(address);

    return user;
  }
}

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