Builder Design Pattern in Java

INTRODUCTION

In the real world, a product built with two or more parts which may be complex or simple in nature. The builder pattern helps to build a complex product by building it's parts (may be simple) one by one (should maintain the order).

USECASE

Assembling a bike with its components like Engine, Wheel, and Gear etc.,

IMPLEMENTATION

Lets us create Model Class - Bike.

public class Bike {  private String wheelType;  private String engineType;  private int cost;  //getters and setters }

The process of assembling a new bike will have set of activities. So my Builder class will have the following activities.

public interface BikeBuilder {  void assembleEngine();  void assembleWheel();  void estimateCost();  Bike getBike(); }

Now implement the BikeBuilder and create different bikes like HeroBike, RoyalEnfield Bike.

public class HeroBike implements BikeBuilder {  private Bike bike;  HeroBike() {    bike = new Bike();  }  @Override  public void assembleWheel() {    bike.setWheelType("Alloy");  }  @Override  public void estimateCost() {    bike.setCost(50000);  }  @Override  public void assembleEngine() {    bike.setEngineType("Petrol");  }  @Override  public Bike getBike() {    return bike;  } }

Actually, the assembling of a bike will be done in a factory where the activities have done one by one sequentially. So create a factory.

public class BikeFactory {  public void assemble(BikeBuilder bikeAssembler) {    bikeAssembler.assembleWheel();    bikeAssembler.assembleEngine();    bikeAssembler.estimateCost();  } }

Now time to test the builder pattern.

public class BuilderPatternTest {  public static void main(String[] args) {    BikeBuilder assembler = null;    BikeFactory bikeFactory = new BikeFactory();    // Hero Bike    System.out.println("=========HERO BIKE======");    assembler = new HeroBike();    bikeFactory.assemble(assembler);    Bike heroBike = assembler.getBike();    System.out.println("Cost: " + heroBike.getCost());    System.out.println("Engine Type: " + heroBike.getEngineType());    // Yamaha Bike    System.out.println("=========ROYAL ENFIELD BIKE=====");    assembler = new RoyalEnfield();    bikeFactory.assemble(assembler);    Bike yamahaBike = assembler.getBike();    System.out.println("Cost: " + yamahaBike.getCost());    System.out.println("Engine Type: " + yamahaBike.getEngineType());  } }

OUTPUT

=========HERO BIKE=============== Cost: 50000 Engine Type: Petrol =========ROYAL ENFIELD BIKE=============== Cost: 170000 Engine Type: Diesel

Complete Source Code

Hope this example clarifies the Builder Design Pattern. Please share your thoughts in the comments box.

Happy Knowledge Sharing!!!