Java ProgrammingUnderstanding Builder Pattern in Java and J2EE

Understanding Builder Pattern in Java and J2EE

Understanding Builder Pattern

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.
builder_pattern_demo
• 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<Product> products = new ArrayList<Product>();	

	   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.

1 COMMENT

  1. Informative and Insightful blog!

    You have provided a great insight here about builder design pattern in java. Designer pattern allows to develop complicated object phase by phase and also makes sure a way to develop an object as a finished object. It is very helpful for all java developers to know about builder pattern in java, i have enjoyed this blog, thanks a lot for sharing!

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