Design Patterns - Builder Pattern

Builder pattern builds a complex object using simple objects and using a step by step approach. This type of design pattern comes under creational pattern as this pattern provides one of the best ways to create an object.

A Builder class builds the final object step by step. This builder is independent of other objects.

Implementation

We have considered a business case of fast-food restaurant where a typical meal could be a burger and a cold drink. Burger could be either a Veg Burger or Chicken Burger and will be packed by a wrapper. Cold drink could be either a coke or pepsi and will be packed in a bottle.

We are going to create an Item interface representing food items such as burgers and cold drinks and concrete classes implementing the Item interface and a Packing interface representing packaging of food items and concrete classes implementing the Packing interface as burger would be packed in wrapper and cold drink would be packed as bottle.

We then create a Meal class having ArrayList of Item and a MealBuilder to build different types of Meal objects by combining Item. BuilderPatternDemo, our demo class will use MealBuilder to build a Meal.

Step 1

Create an interface Item representing food item and packing.

Item.java

pubpc interface Item {
   pubpc String name();
   pubpc Packing packing();
   pubpc float price();	
}

Packing.java

pubpc interface Packing {
   pubpc String pack();
}

Step 2

Create concrete classes implementing the Packing interface.

Wrapper.java

pubpc class Wrapper implements Packing {

   @Override
   pubpc String pack() {
      return "Wrapper";
   }
}

Bottle.java

pubpc class Bottle implements Packing {

   @Override
   pubpc String pack() {
      return "Bottle";
   }
}

Step 3

Create abstract classes implementing the item interface providing default functionapties.

Burger.java

pubpc abstract class Burger implements Item {

   @Override
   pubpc Packing packing() {
      return new Wrapper();
   }

   @Override
   pubpc abstract float price();
}

ColdDrink.java

pubpc abstract class ColdDrink implements Item {

	@Override
	pubpc Packing packing() {
       return new Bottle();
	}

	@Override
	pubpc abstract float price();
}

Step 4

Create concrete classes extending Burger and ColdDrink classes

VegBurger.java

pubpc class VegBurger extends Burger {

   @Override
   pubpc float price() {
      return 25.0f;
   }

   @Override
   pubpc String name() {
      return "Veg Burger";
   }
}

ChickenBurger.java

pubpc class ChickenBurger extends Burger {

   @Override
   pubpc float price() {
      return 50.5f;
   }

   @Override
   pubpc String name() {
      return "Chicken Burger";
   }
}

Coke.java

pubpc class Coke extends ColdDrink {

   @Override
   pubpc float price() {
      return 30.0f;
   }

   @Override
   pubpc String name() {
      return "Coke";
   }
}

Pepsi.java

pubpc class Pepsi extends ColdDrink {

   @Override
   pubpc float price() {
      return 35.0f;
   }

   @Override
   pubpc String name() {
      return "Pepsi";
   }
}

Step 5

Create a Meal class having Item objects defined above.

Meal.java

import java.util.ArrayList;
import java.util.List;

pubpc class Meal {
   private List<Item> items = new ArrayList<Item>();	

   pubpc void addItem(Item item){
      items.add(item);
   }

   pubpc float getCost(){
      float cost = 0.0f;
      
      for (Item item : items) {
         cost += item.price();
      }		
      return cost;
   }

   pubpc void showItems(){
   
      for (Item item : items) {
         System.out.print("Item : " + item.name());
         System.out.print(", Packing : " + item.packing().pack());
         System.out.println(", Price : " + item.price());
      }		
   }	
}

Step 6

Create a MealBuilder class, the actual builder class responsible to create Meal objects.

MealBuilder.java

pubpc class MealBuilder {

   pubpc Meal prepareVegMeal (){
      Meal meal = new Meal();
      meal.addItem(new VegBurger());
      meal.addItem(new Coke());
      return meal;
   }   

   pubpc Meal prepareNonVegMeal (){
      Meal meal = new Meal();
      meal.addItem(new ChickenBurger());
      meal.addItem(new Pepsi());
      return meal;
   }
}

Step 7

BuiderPatternDemo uses MealBuider to demonstrate builder pattern.

BuilderPatternDemo.java

pubpc class BuilderPatternDemo {
   pubpc static void main(String[] args) {
   
      MealBuilder mealBuilder = new MealBuilder();

      Meal vegMeal = mealBuilder.prepareVegMeal();
      System.out.println("Veg Meal");
      vegMeal.showItems();
      System.out.println("Total Cost: " + vegMeal.getCost());

      Meal nonVegMeal = mealBuilder.prepareNonVegMeal();
      System.out.println("

Non-Veg Meal");
      nonVegMeal.showItems();
      System.out.println("Total Cost: " + nonVegMeal.getCost());
   }
}

Step 8

Verify the output.

Veg Meal
Item : Veg Burger, Packing : Wrapper, Price : 25.0
Item : Coke, Packing : Bottle, Price : 30.0
Total Cost: 55.0


Non-Veg Meal
Item : Chicken Burger, Packing : Wrapper, Price : 50.5
Item : Pepsi, Packing : Bottle, Price : 35.0
Total Cost: 85.5