The Builder Pattern of JAVA Design Patterns

The Builder Pattern uses multiple simple objects to build a complex object step by step. This type of design pattern is a creational pattern, which provides an optimal way to create objects.

Advantages:  1. The builder is independent and easy to expand. 2. It is easy to control the risk of details.

Disadvantages:  1. The products must have something in common, and the scope is limited. 2. If the internal changes are complicated, there will be many construction types.

Usage scenarios:  1. The objects to be generated have complex internal structures. 2. The internal properties of the objects that need to be generated are mutually dependent on each other.

Note: The difference from the factory mode is that the builder mode is more concerned with the order of assembly of parts.

Let's assume a business case for a fast food restaurant, where a typical meal can be a burger and a cold drink. Burgers can be either Veg Burger or Chicken Burger, and they come in a carton. Cold drinks can be Coca-Cola (coke) or Pepsi (pepsi), they are bottled.

//create an object class

public interface Item {

   public String name();
   public Packing packing();
   public float price();   
}

//Create a wrapper class
public interface Packing {
   public String pack();
}


//The wrapper class implements the wrapper interface
public class Wrapper implements Packing {

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

//The bottle class implements the packaging interface
public class Bottle implements Packing {

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


//Create an abstract class to implement the entity class (because the concrete entity class does not know)
public abstract class Burger implements Item {

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

   @Override
   public abstract float price();}

//Create a cold drink entity class
public abstract class ColdDrink implements Item {

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

    @Override
    public abstract float price();}


//Create a veggie burger inheriting from the hamburger class
public class VegBurger extends Burger {

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

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

//Create a chicken burger to implement the burger class

public class ChickenBurger extends Burger {

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

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

//Create a Coca-Cola implementation of the cold drink class
public class Coke extends ColdDrink {

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

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

//Create a Pepsi to implement the cold drink class
public class Pepsi extends ColdDrink {

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

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

//Food class (drinks and hamburgers)
import java.util.ArrayList; import java.util.List;

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

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

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

   public 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());
      }       
   }   
}

//create food
public class MealBuilder {

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

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

//accomplish
public class BuilderPatternDemo {
   public 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("\n\nNon-Veg Meal");
      nonVegMeal.showItems();
      System.out.println("Total Cost: " +nonVegMeal.getCost());
   }}