In the last chapter, we discussed the Factory Pattern, which is one of the most commonly used design patterns in Java/J2EE. In this chapter, we are going to discuss the Builder Pattern which is used to build a complex object from the simple objects through a step by step approach. It falls under the category of creational design pattern as this pattern help us provide a common and very simple way to create a complex object from simple objects. In this pattern, the final object is built by a Builder class through a step by step approach that is independent of other objects.

Implementation of Builder Pattern
To understand the implementation of a builder pattern, lets take an example of a Pizza restaurant that serves pizza and a drink as a lunch meal. Further a served pizza could be a veggie pizza or a cheese pizza packaged in a wrapper. Similarly, a served drink could be a mineral water or a soda drink packaged in a bottle or can. We have to create the following classes and interfaces in order to prepare a Builder Pattern for this pizza restaurant.

• A product interface which represents food products such as pizzas and drinks.
• A Wrapping interface which represents packaging of the food items
• The concrete classes which implement the product and Wrapping interfaces.
• The classes which implement the Wrapping interface as pizza would be packed in wrapped package and drink would be packed as a drink glass.
• A LunchMeal class that has an ArrayList of products.
• A LunchMealBuilder class to build different types of LunchMeal objects by combining products such as Veggie pizza with Mineral water, Veggie pizza with Soda drink, etc.
• A BuilderPatternDemonstration class which will use the LunchMealBuilder class to build a LunchMeal and generate the final bill along with the GST charges.

In the following example, we have demonstrated the above steps to explain the builder pattern in a very simple way.

Step 1: – Creation of an interface Product that represents the food and its wrapping.
Product.java

package com.eduonix.design.pattern.product;

/**
 * 
 * @author Aparajita
 *
 */
public interface Product {
	
	public String productName();

	public Wrapping productWrap();

	public float productPrice();
}

Wrapping.java

package com.eduonix.design.pattern.product;

/**
 * 
 * @author Aparajita
 *
 */
public interface Wrapping {
	
	public String wrap();
	
}

Step 2: – Creation of the concrete classes which implement the Wrapping interface.

PanTray.java

package com.eduonix.design.pattern.pizza;

import com.eduonix.design.pattern.product.Wrapping;

/**
 * 
 * @author Aparajita
 *
 */
public class PanTray implements Wrapping {
	@Override
	public String wrap() {
		return "Presenting Pan tray!";
	}
}

DrinkGlass.java

package com.eduonix.design.pattern.drink;

import com.eduonix.design.pattern.product.Wrapping;

/**
 * 
 * @author Aparajita
 *
 */
public class DrinkGlass implements Wrapping {
	@Override
	public String wrap() {
		return "Glass Drink!";
	}
}

Step 3: – Creation of the abstract classes which implement the product interface providing the default functionalities.

Pizza.java

package com.eduonix.design.pattern.pizza;

import com.eduonix.design.pattern.product.Product;
import com.eduonix.design.pattern.product.Wrapping;

/**
 * 
 * @author Aparajita
 *
 */
public abstract class Pizza implements Product{
	
	   @Override
	   public Wrapping productWrap() {
	      return new PanTray();
	   }

	   @Override
	   public abstract float productPrice();
}

Drink.java

package com.eduonix.design.pattern.drink;

import com.eduonix.design.pattern.product.Product;
import com.eduonix.design.pattern.product.Wrapping;

/**
 * 
 * @author Aparajita
 *
 */
public abstract class Drink implements Product {

	@Override
	public Wrapping productWrap() {
       return new DrinkGlass();
	}

	@Override
	public abstract float productPrice();

}

Step 4: – Creation of the concrete classes extending Pizza and Drink classes.

VeggiePizza.java

package com.eduonix.design.pattern.pizza;

/**
 * 
 * @author Aparajita
 *
 */
public class VeggiePizza extends Pizza{

	   @Override
	   public float productPrice() {
	      return 12.99f;
	   }

	   @Override
	   public String productName() {
	      return "Veggie Pizza!";
	   }
}

CheesePizza.java

package com.eduonix.design.pattern.pizza;

/**
 * 
 * @author Aparajita
 *
 */
public class ChessePizza  extends Pizza{

	   @Override
	   public float productPrice() {
	      return 15.99f;
	   }

	   @Override
	   public String productName() {
	      return "Cheese Pizza!";
	   }
}

MineralWater.java

package com.eduonix.design.pattern.drink;

/**
 * 
 * @author Aparajita
 *
 */
public class MineralWater extends Drink {

	   @Override
	   public float productPrice() {
	      return 0.99f;
	   }

	   @Override
	   public String productName() {
	      return "Mineral Water!";
	   }

}

SodaDrink.java

package com.eduonix.design.pattern.drink;

/**
 * 
 * @author Aparajita
 *
 */
public class SodaDrink extends Drink {

	   @Override
	   public float productPrice() {
	      return 1.99f;
	   }

	   @Override
	   public String productName() {
	      return "Soda Drink!";
	   }


}

Step 5: – Creation of a LunchMeal class which has these product objects.

LunchMeal.java

package com.eduonix.design.pattern.meal;

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

import com.eduonix.design.pattern.product.Product;

/**
 * 
 * @author Aparajita
 *
 */
public class LunchMeal {
	   private List products = new ArrayList();	

	   public void addItem(Product product){
		   products.add(product);
	   }

	   public float getBill(){
	      float bill = 0.0f;
	      
	      for (Product product : products) {
	         bill += product.productPrice();
	      }		
	      /**
	       * GST Calculation 15%
	       */
	      System.out.println("Applied GST is : $"+bill*0.15f); 
	      bill = bill*0.15f + bill;
	      return bill;
	   }

	   public void showProducts(){
	   
	      for (Product product : products) {
	         System.out.print("Product : " + product.productName());
	         System.out.print(", Wrapping : " + product.productWrap().wrap());
	         System.out.println(", Price : $" + product.productPrice());
	      }		
	   }	
}

Step 6: – Creation of a LunchMealBuilder class which is the actual builder class accountable for the creation of LunchMeal objects.

LunchMealBuilder.java

package com.eduonix.design.pattern.meal;

import com.eduonix.design.pattern.drink.MineralWater;
import com.eduonix.design.pattern.drink.SodaDrink;
import com.eduonix.design.pattern.pizza.ChessePizza;
import com.eduonix.design.pattern.pizza.VeggiePizza;

/**
 * 
 * @author Aparajita
 *
 */
public class LunchMealBuilder {

	public LunchMeal prepareVeggiePizzaWithMineralWater() {
		LunchMeal LunchMeal = new LunchMeal();
		LunchMeal.addItem(new VeggiePizza());
		LunchMeal.addItem(new MineralWater());
		return LunchMeal;
	}

	public LunchMeal prepareCheesePizzWithSodaDrink() {
		LunchMeal LunchMeal = new LunchMeal();
		LunchMeal.addItem(new ChessePizza());
		LunchMeal.addItem(new SodaDrink());
		return LunchMeal;
	}

	public LunchMeal prepareVeggiePizzaWithSodaDrink() {
		LunchMeal LunchMeal = new LunchMeal();
		LunchMeal.addItem(new VeggiePizza());
		LunchMeal.addItem(new SodaDrink());
		return LunchMeal;
	}

	public LunchMeal prepareCheesePizzWithMineralWater() {
		LunchMeal LunchMeal = new LunchMeal();
		LunchMeal.addItem(new ChessePizza());
		LunchMeal.addItem(new MineralWater());
		return LunchMeal;
	}
}

Step 7: – Creation of the BuiderPatternDemonstration class which uses LunchMealBuilder class to demonstrate the actual builder pattern.

BuiderPatternDemonstration.java

package com.eduonix.design.pattern;

import com.eduonix.design.pattern.meal.LunchMeal;
import com.eduonix.design.pattern.meal.LunchMealBuilder;

/**
 * 
 * @author Aparajita
 *
 */
public class BuilderPatternDemonstration {
	public static void main(String[] args) {

		LunchMealBuilder lunchMealBuilder = new LunchMealBuilder();

		LunchMeal veggiePizzaMealMW = lunchMealBuilder.prepareVeggiePizzaWithMineralWater();
		System.out.println("Veggie Pizza Meal with Mineral Water");
		veggiePizzaMealMW.showProducts();
		System.out.println("Total Bill: $" + veggiePizzaMealMW.getBill());
		System.out.println("------------------------------"); 

		LunchMeal veggiePizzaMealSD = lunchMealBuilder.prepareVeggiePizzaWithSodaDrink();
		System.out.println("Veggie Pizza Meal with Soft Drink");
		veggiePizzaMealSD.showProducts();
		System.out.println("Total Bill: $" + veggiePizzaMealSD.getBill());
		System.out.println("-----------------------------"); 
		
		LunchMeal cheesePizzaMealMW = lunchMealBuilder.prepareCheesePizzWithMineralWater();
		System.out.println("Cheese Pizza Meal with Mineral Water");
		cheesePizzaMealMW.showProducts();
		System.out.println("Total Bill: $" + cheesePizzaMealMW.getBill());
		System.out.println("-----------------------------"); 
		
		LunchMeal cheesePizzaMealSD = lunchMealBuilder.prepareCheesePizzWithSodaDrink();
		System.out.println("Cheese Pizza Meal with Soda Drink");
		cheesePizzaMealSD.showProducts();
		System.out.println("Total Bill: $" + cheesePizzaMealSD.getBill());
		System.out.println("-----------------------------"); 
	}
}

Output: – When we execute the above BuiderPatternDemonstration class as a Java Application, we can observe the following output.

Veggie Pizza Meal with Mineral Water
Product : Veggie Pizza!, Wrapping : Presenting Pan tray!, Price : $12.99
Product : Mineral Water!, Wrapping : Glass Drink!, Price : $0.99
Applied GST is : $2.0970001
Total Bill: $16.077
------------------------------
Veggie Pizza Meal with Soft Drink
Product : Veggie Pizza!, Wrapping : Presenting Pan tray!, Price : $12.99
Product : Soda Drink!, Wrapping : Glass Drink!, Price : $1.99
Applied GST is : $2.247
Total Bill: $17.227
-----------------------------
Cheese Pizza Meal with Mineral Water
Product : Cheese Pizza!, Wrapping : Presenting Pan tray!, Price : $15.99
Product : Mineral Water!, Wrapping : Glass Drink!, Price : $0.99
Applied GST is : $2.547
Total Bill: $19.527
-----------------------------
Cheese Pizza Meal with Soda Drink
Product : Cheese Pizza!, Wrapping : Presenting Pan tray!, Price : $15.99
Product : Soda Drink!, Wrapping : Glass Drink!, Price : $1.99
Applied GST is : $2.697
Total Bill: $20.677

Source code for builder pattern in Java & J2EE

Conclusion: –
In this chapter, we discussed the builder pattern in detail along with suitable examples. In the example, we have demonstrated the building of a complex object from the simple objects through a step by step approach.

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