Decorator Blueprint Pattern Inwards Coffee Amongst Example

The Decorator blueprint Pattern is i of the famous Gang of Four (GOF) structural blueprint pattern, which provides a dynamic way of extending an object's functionality. It's unlike than the traditional way of adding novel functionality into an object using Inheritance, instead, it uses Composition which makes it flexible together with allows to add together novel functionalities at the run time, every bit reverse to Inheritance, which adds new functionality at compile time. Because of this flexibility, Decorator is i of the darling patterns for many Java developer. Btw, similar many others object-oriented blueprint patterns, the decorator blueprint pattern is introduced yesteryear the famous Gang of Four blueprint pattern book, almost ii decades ago. This agency it's a time-tested way of adding novel functionalities into an object.

In this Java blueprint pattern tutorial, nosotros volition larn the Decorator blueprint pattern yesteryear using it inwards a Java example. This is the best way of learning blueprint pattern, followed you lot endeavour it yourself to apply inwards similar scenarios. 

The decorator pattern is i of the pop blueprint patterns along amongst the Factory method pattern together with Singleton Pattern, together with you lot tin run across it's usage fifty-fifty inwards JDK itself. A duet of classes from the java.io packet like BufferedInputStream, LineNumberInputStream are a practiced instance of Decorator blueprint pattern inwards Java. 

Btw, if you lot are novel into blueprint pattern world, together with thence I too propose you lot check The Java Design Patterns Masterclass which non solely covers Decorator pattern but too other GOF patterns. It was too latterly been updated to encompass Java SE 8 implementation every bit well.

Decorator Design Pattern inwards Java

In lodge to present you, how to implement a Decorator pattern, permit me starting fourth dimension explicate requirements. Do nosotros demand to create software for calculating the toll for a Sandwich, yummy... no? Since the client tin customize a sandwich yesteryear asking extra cheese or extra fillings, you lot too demand to include the cost of those items inwards the in conclusion toll of Sandwich. 

Since this customization tin vary a lot amid unlike customers together with offering from a shop, creating classes for unlike types of Sandwich amongst unlike fillings or extras like BrownBreadSandWithCheese or WhiteBreaSandwitchWithCheeseAndTomato volition but clutter the code amongst lots of endless pocket-sized classes. 

Now this work looks a natural tally for applying Decorator pattern because nosotros receive got a base of operations object Sandwich, which tin live on decorated amongst extra cheese together with fillings. By using the Decorator pattern, you lot tin extend the functionality of Sandwich class at runtime, based upon customer's request, which is impossible amongst Inheritance until you lot receive got a specific course of report for every possible client request. 

This is too i of the reasons why Composition is preferred over Inheritance inwards Object-oriented blueprint together with especially inwards Java. 

Now, let's run across our course of report structure, We receive got an abstract course of report Sandwich, amongst abstract method price() together with a concrete implementation course of report WhiteBreadSandwich, which cost $3.0. 

Now, inwards lodge to render extra cheese, which manifestly incurs extra cost, nosotros are going to utilisation the Decorator blueprint pattern. We receive got a Decorator abstract class, which volition deed every bit a base of operations for Decorators called SandwichDecorator, together with a concrete implementation of this every bit CheeseDecorator.

SandwichDecorator extends Sandwich, to live on of the same type every bit the original object, which is getting decorated. This is a critical requirement of Decorator pattern thence that a decorated object tin stand upwards inwards house of the original object similar it tin live on passed when a method expects the original object. 

Decorator adds functionality earlier or afterwards delegating the chore to the original object, which agency inwards this instance toll of a WhilteBreadSandwich with Cheese volition live on calculated yesteryear the starting fourth dimension calculating toll of WhiteBreadSandwich together with and thence the toll of Cheese. 

Finally, I receive got a course of report called SandwichMaker, which volition brand a delicious sandwich for you lot :) I hateful it volition attempt the whole plan together with demonstrate how Decorator pattern adds novel functionality on the wing at runtime. 

I receive got too used BigDecimal to stand upwards for coin instead of double primitive to follow best practices suggested inwards Effective Java. If you lot don't know why to read this Java error virtually using double to stand upwards for the price

UML diagram of Decorator Pattern

Here is the UML course of report diagram of the decorator blueprint pattern. You tin run across that nosotros receive got a Component interface, which is used to create ConcreteComponents. In our real-world example, Sandwich is a gene interface together with WhiteBreadSandwich is a concrete component. 

Now if nosotros desire to add together an additional characteristic to the Component interface, nosotros create around other interface called Decorator, which inherit Component interface, this is rattling of import because it allows you lot to overstep an event of Decorator to whatever method which accepts an event of the Component interface. 

Now you lot tin create an implementation of a decorator, which has both functionalities provided yesteryear the original interface together with novel characteristic provided yesteryear the decorator. This way you lot tin add together novel features inwards the existing course of report hierarchy without modifying tried together with tested code. 

This is around other argue programmers tell why the composition is ameliorate than Inheritance, but if you lot desire to larn to a greater extent than virtually blueprint principles together with patterns, delight see Eclipse IDE, but create a Java project, select that projection inwards the packet explorer together with re-create the code there, it volition automatically create correct packages together with Java classes. 

Sandwich.java import java.math.BigDecimal;  /**  * Base course of report for all types of Sandwich, cost method is abstract because  * unlike sandwiches has unlike price.  *  * @author Javin Paul  */ public abstract class Sandwich {        protected String description = "Sandwich";           public String getDescription(){         return description;     }         public abstract BigDecimal price(); }   WhiteBreadSandWich.java import java.math.BigDecimal;  /**  * H5N1 Concrete implementation of abstract Sandwich class, which stand upwards for a WhiteBread  * Sandwich, whose toll is 3.0$.  *  * @author Javin Paul  */ public class WhiteBreadSandWich extends Sandwich {         public WhiteBreadSandWich(String desc){        description = desc;     }         @Override     public BigDecimal price() {         return new BigDecimal("3.0");     }     }  SandWichDecorator.java /**  * Base course of report for Decorators, this course of report inherit from Sandwich, thence that  * it tin live on of same type, which is required to overstep decorators where  * original object is expected. Later, this course of report volition too come upwards handy  * to render mutual functionalities to Decorators.  *  * @author  */ public abstract class SandWichDecorator extends Sandwich {           @Override     public abstract BigDecimal price();     }  CheeseDecorator.java import java.math.BigDecimal;  /**  * H5N1 Decorator class, which adds cheese (new functionality) into Sandwich object.  * This Decorator course of report modifies price() together with getDescritption() method to implement  * novel behaviour.  *  * @author  */ public class CheeseDecorator extends SandWichDecorator{     Sandwich currentSandwich;         public CheeseDecorator(Sandwich sw){         currentSandwich = sw;     }         @Override     public String getDescription(){         return currentSandwich.getDescription() + ", Cheese";     }     @Override     public BigDecimal price() {         return currentSandwich.price().add(new BigDecimal("0.50"));     }     }   SandwichMaker.java /**  * Test course of report to demonstrate How Decorator Pattern inwards Java piece of work together. This class  * starting fourth dimension creates a Sandwich together with decorates it amongst extra cheese. This is dainty example  * of how to render novel functionalities to an object at runtime using Decorator Pattern.  *  * @author Javain Paul  */ public class SandwichMaker {         public static void main(String args[]){                 Sandwich mySandwich = new WhiteBreadSandWich("White staff of life Sandwich");         System.out.printf("Price of %s is $%.2f %n", mySandwich.getDescription(), 

                                                     mySandwich.price());                 //adding extra cheese using Decorator Pattter         mySandwich = new CheeseDecorator(mySandwich);         System.out.printf("Price of %s is $%.2f %n", mySandwich.getDescription(), 

                                                     mySandwich.price());     } }  Output: Price of White staff of life Sandwich is $3.00 Price of White staff of life Sandwich, Cheese is $3.50

You tin run across that straight off toll is easily calculated based upon the toppings together with extras you lot add together on Sandwich. These blueprint patterns are rattling useful for writing code which tin withstand the attempt of fourth dimension together with that's why every serious programmer should larn patterns. If you lot desire to larn to a greater extent than virtually other OOP blueprint pattern similar Decorator together with thence you lot tin bring a aspect at the interface of the object or yesteryear extending an abstract class of the original class.

2) The decorator pattern is based on Composition, which agency it needs an original object to decorate it. This is achieved yesteryear creating a constructor on decorator course of report which accepts a base of operations type of original object. similar inwards this instance constructor of CheeseDecorator accepts Sandwich object. 

3) Decorator course of report adds novel functionality earlier or afterwards delegating the chore to the original object. In this example, the toll of Decorator i.e. cheese is included afterwards calculating the toll of White Bread Sandwich.

4) The decorator pattern is too a practiced instance of Open Closed blueprint principle, which is i of the cardinal principles from Uncle Bob's SOLID blueprint principles. If you lot desire to larn to a greater extent than virtually SOLID principles, delight banking venture check the courses)

Difference betwixt Factory together with Dependency Injection Pattern? (answer)

How to create thread-safe Singleton inwards Java? (example)

How to implement the Strategy Design Pattern inwards Java? (example)

Difference betwixt Factory together with AbstractFactory Pattern? (example)

18 Java Design Pattern Interview Questions amongst Answers (list)

Difference betwixt Factory together with Abstract Factory pattern inwards Java (answer)

How to blueprint a Vending Machine inwards Java? (questions)

20 System Design Interview Questions (list)

How to acquire a method of HashMap industrial plant internally inwards Java? (answer)

Difference betwixt Abstraction together with Encapsulation inwards Java? (answer)

Difference betwixt State together with Strategy Design Pattern inwards Java? (answer)

Top five Courses to larn Design Patterns inwards Java (courses)

5 Free Courses to larn Data Structure together with Algorithms (courses)

Thanks a lot for reading this article thence far. If you lot similar this Decorator blueprint pattern tutorial inwards Java together with thence delight part amongst your friends together with colleagues. If you lot receive got whatever questions or feedback together with thence delight drib a note.

P. S. - If you lot desire to larn to a greater extent than virtually blueprint patterns together with how they tin aid you lot to write ameliorate code inwards Java, I propose you lot bring a aspect at the Java Design Patterns together with Architecture - a Free course of report on Udemy.

Share this post