Category: 03. Design Patterns

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Proxy Pattern

In proxy pattern, a class represents functionality of another class. This type of design pattern comes under structural pattern.

In proxy pattern, we create object having original object to interface its functionality to outer world.

Implementation

We are going to create an Image interface and concrete classes implementing the Image interface. ProxyImage is a a proxy class to reduce memory footprint of RealImage object loading.

ProxyPatternDemo, our demo class, will use ProxyImage to get an Image object to load and display as it needs.

Step 1

Create an interface.

Image.java

public interface Image {
   void display();
}

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Step 2

Create concrete classes implementing the same interface.

RealImage.java

public class RealImage implements Image {

   private String fileName;

   public RealImage(String fileName){
  this.fileName = fileName;
  loadFromDisk(fileName);   }

   @Override
   public void display() {
  System.out.println("Displaying " + fileName);   }

   private void loadFromDisk(String fileName){
  System.out.println("Loading " + fileName);   }
}

ProxyImage.java

public class ProxyImage implements Image{

   private RealImage realImage;
   private String fileName;

   public ProxyImage(String fileName){
  this.fileName = fileName;   }

   @Override
   public void display() {
  if(realImage == null){
     realImage = new RealImage(fileName);
  }
  realImage.display();   }
}

Step 3

Use the ProxyImage to get object of RealImage class when required.

ProxyPatternDemo.java

public class ProxyPatternDemo {
	
   public static void main(String[] args) {
  Image image = new ProxyImage("test_10mb.jpg");
  //image will be loaded from disk
  image.display(); 
  System.out.println("");
  
  //image will not be loaded from disk
  image.display(); 	   }
}

Step 4

Verify the output.

Loading test_10mb.jpg
Displaying test_10mb.jpg

Displaying test_10mb.jpg

August 31, 2024

Flyweight pattern is primarily used to reduce the number of objects created and to decrease memory footprint and increase performance. This type of design pattern comes under structural pattern as this pattern provides ways to decrease object count thus improving the object structure of application.

Flyweight pattern tries to reuse already existing similar kind objects by storing them and creates new object when no matching object is found. We will demonstrate this pattern by drawing 20 circles of different locations but we will create only 5 objects. Only 5 colors are available so color property is used to check already existing Circle objects.

Implementation

We are going to create a Shape interface and concrete class Circle implementing the Shape interface. A factory class ShapeFactory is defined as a next step.

ShapeFactory has a HashMap of Circle having key as color of the Circle object. Whenever a request comes to create a circle of particular color to ShapeFactory, it checks the circle object in its HashMap, if object of Circle found, that object is returned otherwise a new object is created, stored in hashmap for future use, and returned to client.

FlyWeightPatternDemo, our demo class, will use ShapeFactory to get a Shape object. It will pass information (red / green / blue/ black / white) to ShapeFactory to get the circle of desired color it needs.

Step 1

Create an interface.

Shape.java

public interface Shape {
   void draw();
}

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Step 2

Create concrete class implementing the same interface.

Circle.java

public class Circle implements Shape {
   private String color;
   private int x;
   private int y;
   private int radius;

   public Circle(String color){
  this.color = color;		   }

   public void setX(int x) {
  this.x = x;   }

   public void setY(int y) {
  this.y = y;   }

   public void setRadius(int radius) {
  this.radius = radius;   }

   @Override
   public void draw() {
  System.out.println("Circle: Draw() &#91;Color : " + color + ", x : " + x + ", y :" + y + ", radius :" + radius);   }
}

Step 3

Create a factory to generate object of concrete class based on given information.

ShapeFactory.java

import java.util.HashMap;

public class ShapeFactory {

   // Uncomment the compiler directive line and
   // javac *.java will compile properly.
   // @SuppressWarnings("unchecked")
   private static final HashMap circleMap = new HashMap();

   public static Shape getCircle(String color) {
  Circle circle = (Circle)circleMap.get(color);
  if(circle == null) {
     circle = new Circle(color);
     circleMap.put(color, circle);
     System.out.println("Creating circle of color : " + color);
  }
  return circle;   }
}

Step 4

Use the factory to get object of concrete class by passing an information such as color.

FlyweightPatternDemo.java

public class FlyweightPatternDemo {
   private static final String colors[] = { "Red", "Green", "Blue", "White", "Black" };
   public static void main(String[] args) {

  for(int i=0; i &lt; 20; ++i) {
     Circle circle = (Circle)ShapeFactory.getCircle(getRandomColor());
     circle.setX(getRandomX());
     circle.setY(getRandomY());
     circle.setRadius(100);
     circle.draw();
  }   }
   private static String getRandomColor() {
  return colors&#91;(int)(Math.random()*colors.length)];   }
   private static int getRandomX() {
  return (int)(Math.random()*100 );   }
   private static int getRandomY() {
  return (int)(Math.random()*100);   }
}

Step 5

Verify the output.

Creating circle of color : Black
Circle: Draw() [Color : Black, x : 36, y :71, radius :100
Creating circle of color : Green
Circle: Draw() [Color : Green, x : 27, y :27, radius :100
Creating circle of color : White
Circle: Draw() [Color : White, x : 64, y :10, radius :100
Creating circle of color : Red
Circle: Draw() [Color : Red, x : 15, y :44, radius :100
Circle: Draw() [Color : Green, x : 19, y :10, radius :100
Circle: Draw() [Color : Green, x : 94, y :32, radius :100
Circle: Draw() [Color : White, x : 69, y :98, radius :100
Creating circle of color : Blue
Circle: Draw() [Color : Blue, x : 13, y :4, radius :100
Circle: Draw() [Color : Green, x : 21, y :21, radius :100
Circle: Draw() [Color : Blue, x : 55, y :86, radius :100
Circle: Draw() [Color : White, x : 90, y :70, radius :100
Circle: Draw() [Color : Green, x : 78, y :3, radius :100
Circle: Draw() [Color : Green, x : 64, y :89, radius :100
Circle: Draw() [Color : Blue, x : 3, y :91, radius :100
Circle: Draw() [Color : Blue, x : 62, y :82, radius :100
Circle: Draw() [Color : Green, x : 97, y :61, radius :100
Circle: Draw() [Color : Green, x : 86, y :12, radius :100
Circle: Draw() [Color : Green, x : 38, y :93, radius :100
Circle: Draw() [Color : Red, x : 76, y :82, radius :100
Circle: Draw() [Color : Blue, x : 95, y :82, radius :100

August 31, 2024

Facade Pattern

Facade pattern hides the complexities of the system and provides an interface to the client using which the client can access the system. This type of design pattern comes under structural pattern as this pattern adds an interface to existing system to hide its complexities.

This pattern involves a single class which provides simplified methods required by client and delegates calls to methods of existing system classes.

Implementation

We are going to create a Shape interface and concrete classes implementing the Shape interface. A facade class ShapeMaker is defined as a next step.

ShapeMaker class uses the concrete classes to delegate user calls to these classes. FacadePatternDemo, our demo class, will use ShapeMaker class to show the results.

Step 1

Create an interface.

Shape.java

public interface Shape {
   void draw();
}

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Step 2

Create concrete classes implementing the same interface.

Rectangle.java

public class Rectangle implements Shape {

   @Override
   public void draw() {
  System.out.println("Rectangle::draw()");   }
}

Square.java

public class Square implements Shape {

   @Override
   public void draw() {
  System.out.println("Square::draw()");   }
}

Circle.java

public class Circle implements Shape {

   @Override
   public void draw() {
  System.out.println("Circle::draw()");   }
}

Step 3

Create a facade class.

ShapeMaker.java

public class ShapeMaker {
   private Shape circle;
   private Shape rectangle;
   private Shape square;

   public ShapeMaker() {
  circle = new Circle();
  rectangle = new Rectangle();
  square = new Square();   }

   public void drawCircle(){
  circle.draw();   }
   public void drawRectangle(){
  rectangle.draw();   }
   public void drawSquare(){
  square.draw();   }
}

Step 4

Use the facade to draw various types of shapes.

FacadePatternDemo.java

public class FacadePatternDemo {
   public static void main(String[] args) {
  ShapeMaker shapeMaker = new ShapeMaker();
  shapeMaker.drawCircle();
  shapeMaker.drawRectangle();
  shapeMaker.drawSquare();		   }
}

Step 5

Verify the output.

Circle::draw()
Rectangle::draw()
Square::draw()

August 31, 2024

Decorator Pattern

Decorator pattern allows a user to add new functionality to an existing object without altering its structure. This type of design pattern comes under structural pattern as this pattern acts as a wrapper to existing class.

This pattern creates a decorator class which wraps the original class and provides additional functionality keeping class methods signature intact.

We are demonstrating the use of decorator pattern via following example in which we will decorate a shape with some color without alter shape class.

Implementation

We’re going to create a Shape interface and concrete classes implementing the Shape interface. We will then create an abstract decorator class ShapeDecorator implementing the Shape interface and having Shape object as its instance variable.

RedShapeDecorator is concrete class implementing ShapeDecorator.

DecoratorPatternDemo, our demo class will use RedShapeDecorator to decorate Shape objects.

Step 1

Create an interface.

Shape.java

public interface Shape {
   void draw();
}

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Step 2

Create concrete classes implementing the same interface.

Rectangle.java

public class Rectangle implements Shape {

   @Override
   public void draw() {
  System.out.println("Shape: Rectangle");   }
}

Circle.java

public class Circle implements Shape {

   @Override
   public void draw() {
  System.out.println("Shape: Circle");   }
}

Step 3

Create abstract decorator class implementing the Shape interface.

ShapeDecorator.java

public abstract class ShapeDecorator implements Shape {
   protected Shape decoratedShape;

   public ShapeDecorator(Shape decoratedShape){
  this.decoratedShape = decoratedShape;   }

   public void draw(){
  decoratedShape.draw();   }	
}

Step 4

Create concrete decorator class extending the ShapeDecorator class.

RedShapeDecorator.java

public class RedShapeDecorator extends ShapeDecorator {

   public RedShapeDecorator(Shape decoratedShape) {
  super(decoratedShape);		   }

   @Override
   public void draw() {
  decoratedShape.draw();	       
  setRedBorder(decoratedShape);   }

   private void setRedBorder(Shape decoratedShape){
  System.out.println("Border Color: Red");   }
}

Step 5

Use the RedShapeDecorator to decorate Shape objects.

DecoratorPatternDemo.java

public class DecoratorPatternDemo {
   public static void main(String[] args) {

  Shape circle = new Circle();
  Shape redCircle = new RedShapeDecorator(new Circle());
  Shape redRectangle = new RedShapeDecorator(new Rectangle());
  System.out.println("Circle with normal border");
  circle.draw();
  System.out.println("\nCircle of red border");
  redCircle.draw();
  System.out.println("\nRectangle of red border");
  redRectangle.draw();   }
}

Step 6

Verify the output.

Circle with normal border
Shape: Circle

Circle of red border
Shape: Circle
Border Color: Red

Rectangle of red border
Shape: Rectangle
Border Color: Red

August 31, 2024

Composite Pattern

Composite pattern is used where we need to treat a group of objects in similar way as a single object. Composite pattern composes objects in term of a tree structure to represent part as well as whole hierarchy. This type of design pattern comes under structural pattern as this pattern creates a tree structure of group of objects.

This pattern creates a class that contains group of its own objects. This class provides ways to modify its group of same objects.

We are demonstrating use of composite pattern via following example in which we will show employees hierarchy of an organization.

Implementation

We have a class Employee which acts as composite pattern actor class. CompositePatternDemo, our demo class will use Employee class to add department level hierarchy and print all employees.

Step 1

Create Employee class having list of Employee objects.

Employee.java

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

public class Employee {
   private String name;
   private String dept;
   private int salary;
   private List<Employee> subordinates;

   // constructor
   public Employee(String name,String dept, int sal) {
  this.name = name;
  this.dept = dept;
  this.salary = sal;
  subordinates = new ArrayList&lt;Employee&gt;();   }

   public void add(Employee e) {
  subordinates.add(e);   }

   public void remove(Employee e) {
  subordinates.remove(e);   }

   public List<Employee> getSubordinates(){
 return subordinates;   }

   public String toString(){
  return ("Employee :&#91; Name : " + name + ", dept : " + dept + ", salary :" + salary+" ]");   }   
}

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Step 2

Use the Employee class to create and print employee hierarchy.

CompositePatternDemo.java

public class CompositePatternDemo {
   public static void main(String[] args) {
   
  Employee CEO = new Employee("John","CEO", 30000);
  Employee headSales = new Employee("Robert","Head Sales", 20000);
  Employee headMarketing = new Employee("Michel","Head Marketing", 20000);
  Employee clerk1 = new Employee("Laura","Marketing", 10000);
  Employee clerk2 = new Employee("Bob","Marketing", 10000);
  Employee salesExecutive1 = new Employee("Richard","Sales", 10000);
  Employee salesExecutive2 = new Employee("Rob","Sales", 10000);
  CEO.add(headSales);
  CEO.add(headMarketing);
  headSales.add(salesExecutive1);
  headSales.add(salesExecutive2);
  headMarketing.add(clerk1);
  headMarketing.add(clerk2);
  //print all employees of the organization
  System.out.println(CEO); 
  
  for (Employee headEmployee : CEO.getSubordinates()) {
     System.out.println(headEmployee);
     
     for (Employee employee : headEmployee.getSubordinates()) {
        System.out.println(employee);
     }
  }		   }
}

Step 3

Verify the output.

Employee :[ Name : John, dept : CEO, salary :30000 ]
Employee :[ Name : Robert, dept : Head Sales, salary :20000 ]
Employee :[ Name : Richard, dept : Sales, salary :10000 ]
Employee :[ Name : Rob, dept : Sales, salary :10000 ]
Employee :[ Name : Michel, dept : Head Marketing, salary :20000 ]
Employee :[ Name : Laura, dept : Marketing, salary :10000 ]
Employee :[ Name : Bob, dept : Marketing, salary :10000 ]

August 31, 2024

Filter Pattern

Filter pattern or Criteria pattern is a design pattern that enables developers to filter a set of objects using different criteria and chaining them in a decoupled way through logical operations. This type of design pattern comes under structural pattern as this pattern combines multiple criteria to obtain single criteria.

Implementation

We’re going to create a Person object, Criteria interface and concrete classes implementing this interface to filter list of Person objects. CriteriaPatternDemo, our demo class uses Criteria objects to filter List of Person objects based on various criteria and their combinations.

Step 1

Create a class on which criteria is to be applied.

Person.java

public class Person {
	
   private String name;
   private String gender;
   private String maritalStatus;

   public Person(String name, String gender, String maritalStatus){
  this.name = name;
  this.gender = gender;
  this.maritalStatus = maritalStatus;		   }

   public String getName() {
  return name;   }
   public String getGender() {
  return gender;   }
   public String getMaritalStatus() {
  return maritalStatus;   }	
}

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Step 2

Create an interface for Criteria.

Criteria.java

import java.util.List;

public interface Criteria {
   public List<Person> meetCriteria(List<Person> persons);
}

Step 3

Create concrete classes implementing the Criteria interface.

CriteriaMale.java

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

public class CriteriaMale implements Criteria {

   @Override
   public List<Person> meetCriteria(List<Person> persons) {
  List&lt;Person&gt; malePersons = new ArrayList&lt;Person&gt;(); 
  
  for (Person person : persons) {
     if(person.getGender().equalsIgnoreCase("MALE")){
        malePersons.add(person);
     }
  }
  return malePersons;   }
}

CriteriaFemale.java

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

public class CriteriaFemale implements Criteria {

   @Override
   public List<Person> meetCriteria(List<Person> persons) {
  List&lt;Person&gt; femalePersons = new ArrayList&lt;Person&gt;(); 
  
  for (Person person : persons) {
     if(person.getGender().equalsIgnoreCase("FEMALE")){
        femalePersons.add(person);
     }
  }
  return femalePersons;   }
}

CriteriaSingle.java

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

public class CriteriaSingle implements Criteria {

   @Override
   public List<Person> meetCriteria(List<Person> persons) {
  List&lt;Person&gt; singlePersons = new ArrayList&lt;Person&gt;(); 
  
  for (Person person : persons) {
     if(person.getMaritalStatus().equalsIgnoreCase("SINGLE")){
        singlePersons.add(person);
     }
  }
  return singlePersons;   }
}

AndCriteria.java

import java.util.List;

public class AndCriteria implements Criteria {

   private Criteria criteria;
   private Criteria otherCriteria;

   public AndCriteria(Criteria criteria, Criteria otherCriteria) {
  this.criteria = criteria;
  this.otherCriteria = otherCriteria;    }

   @Override
   public List<Person> meetCriteria(List<Person> persons) {
   
  List&lt;Person&gt; firstCriteriaPersons = criteria.meetCriteria(persons);		
  return otherCriteria.meetCriteria(firstCriteriaPersons);   }
}

OrCriteria.java

import java.util.List;

public class OrCriteria implements Criteria {

   private Criteria criteria;
   private Criteria otherCriteria;

   public OrCriteria(Criteria criteria, Criteria otherCriteria) {
  this.criteria = criteria;
  this.otherCriteria = otherCriteria;    }

   @Override
   public List<Person> meetCriteria(List<Person> persons) {
  List&lt;Person&gt; firstCriteriaItems = criteria.meetCriteria(persons);
  List&lt;Person&gt; otherCriteriaItems = otherCriteria.meetCriteria(persons);
  for (Person person : otherCriteriaItems) {
     if(!firstCriteriaItems.contains(person)){
        firstCriteriaItems.add(person);
     }
  }	
  return firstCriteriaItems;   }
}

Step4

Use different Criteria and their combination to filter out persons.

CriteriaPatternDemo.java

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

public class CriteriaPatternDemo {
   public static void main(String[] args) {
  List&lt;Person&gt; persons = new ArrayList&lt;Person&gt;();
  persons.add(new Person("Robert","Male", "Single"));
  persons.add(new Person("John", "Male", "Married"));
  persons.add(new Person("Laura", "Female", "Married"));
  persons.add(new Person("Diana", "Female", "Single"));
  persons.add(new Person("Mike", "Male", "Single"));
  persons.add(new Person("Bobby", "Male", "Single"));
  Criteria male = new CriteriaMale();
  Criteria female = new CriteriaFemale();
  Criteria single = new CriteriaSingle();
  Criteria singleMale = new AndCriteria(single, male);
  Criteria singleOrFemale = new OrCriteria(single, female);
  System.out.println("Males: ");
  printPersons(male.meetCriteria(persons));
  System.out.println("\nFemales: ");
  printPersons(female.meetCriteria(persons));
  System.out.println("\nSingle Males: ");
  printPersons(singleMale.meetCriteria(persons));
  System.out.println("\nSingle Or Females: ");
  printPersons(singleOrFemale.meetCriteria(persons));   }

   public static void printPersons(List<Person> persons){
   
  for (Person person : persons) {
     System.out.println("Person : &#91; Name : " + person.getName() + ", Gender : " + person.getGender() + ", Marital Status : " + person.getMaritalStatus() + " ]");
  }   }      
}

Step 5

Verify the output.

Males: 
Person : [ Name : Robert, Gender : Male, Marital Status : Single ]
Person : [ Name : John, Gender : Male, Marital Status : Married ]
Person : [ Name : Mike, Gender : Male, Marital Status : Single ]
Person : [ Name : Bobby, Gender : Male, Marital Status : Single ]

Females: 
Person : [ Name : Laura, Gender : Female, Marital Status : Married ]
Person : [ Name : Diana, Gender : Female, Marital Status : Single ]

Single Males: 
Person : [ Name : Robert, Gender : Male, Marital Status : Single ]
Person : [ Name : Mike, Gender : Male, Marital Status : Single ]
Person : [ Name : Bobby, Gender : Male, Marital Status : Single ]

Single Or Females: 
Person : [ Name : Robert, Gender : Male, Marital Status : Single ]
Person : [ Name : Diana, Gender : Female, Marital Status : Single ]
Person : [ Name : Mike, Gender : Male, Marital Status : Single ]
Person : [ Name : Bobby, Gender : Male, Marital Status : Single ]
Person : [ Name : Laura, Gender : Female, Marital Status : Married ]

August 31, 2024

Bridge Pattern

Bridge is used when we need to decouple an abstraction from its implementation so that the two can vary independently. This type of design pattern comes under structural pattern as this pattern decouples implementation class and abstract class by providing a bridge structure between them.

This pattern involves an interface which acts as a bridge which makes the functionality of concrete classes independent from interface implementer classes. Both types of classes can be altered structurally without affecting each other.

We are demonstrating use of Bridge pattern via following example in which a circle can be drawn in different colors using same abstract class method but different bridge implementer classes.

Implementation

We have a DrawAPI interface which is acting as a bridge implementer and concrete classes RedCircle, GreenCircle implementing the DrawAPI interface. Shape is an abstract class and will use object of DrawAPI. BridgePatternDemo, our demo class will use Shape class to draw different colored circle.

Step 1

Create bridge implementer interface.

DrawAPI.java

public interface DrawAPI {
   public void drawCircle(int radius, int x, int y);
}

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Step 2

Create concrete bridge implementer classes implementing the DrawAPI interface.

RedCircle.java

public class RedCircle implements DrawAPI {
   @Override
   public void drawCircle(int radius, int x, int y) {
  System.out.println("Drawing Circle&#91; color: red, radius: " + radius + ", x: " + x + ", " + y + "]");   }
}

GreenCircle.java

public class GreenCircle implements DrawAPI {
   @Override
   public void drawCircle(int radius, int x, int y) {
  System.out.println("Drawing Circle&#91; color: green, radius: " + radius + ", x: " + x + ", " + y + "]");   }
}

Step 3

Create an abstract class Shape using the DrawAPI interface.

Shape.java

public abstract class Shape {
   protected DrawAPI drawAPI;
   
   protected Shape(DrawAPI drawAPI){
  this.drawAPI = drawAPI;   }
   public abstract void draw();	
}

Step 4

Create concrete class implementing the Shape interface.

Circle.java

public class Circle extends Shape {
   private int x, y, radius;

   public Circle(int x, int y, int radius, DrawAPI drawAPI) {
  super(drawAPI);
  this.x = x;  
  this.y = y;  
  this.radius = radius;   }

   public void draw() {
  drawAPI.drawCircle(radius,x,y);   }
}

Step 5

Use the Shape and DrawAPI classes to draw different colored circles.

BridgePatternDemo.java

public class BridgePatternDemo {
   public static void main(String[] args) {
  Shape redCircle = new Circle(100,100, 10, new RedCircle());
  Shape greenCircle = new Circle(100,100, 10, new GreenCircle());
  redCircle.draw();
  greenCircle.draw();   }
}

Step 6

Verify the output.

Drawing Circle[ color: red, radius: 10, x: 100, 100]
Drawing Circle[  color: green, radius: 10, x: 100, 100]

August 31, 2024

Adapter Pattern

Adapter pattern works as a bridge between two incompatible interfaces. This type of design pattern comes under structural pattern as this pattern combines the capability of two independent interfaces.

This pattern involves a single class which is responsible to join functionalities of independent or incompatible interfaces. A real life example could be a case of card reader which acts as an adapter between memory card and a laptop. You plugin the memory card into card reader and card reader into the laptop so that memory card can be read via laptop.

We are demonstrating use of Adapter pattern via following example in which an audio player device can play mp3 files only and wants to use an advanced audio player capable of playing vlc and mp4 files.

Implementation

We have a MediaPlayer interface and a concrete class AudioPlayer implementing the MediaPlayer interface. AudioPlayer can play mp3 format audio files by default.

We are having another interface AdvancedMediaPlayer and concrete classes implementing the AdvancedMediaPlayer interface. These classes can play vlc and mp4 format files.

We want to make AudioPlayer to play other formats as well. To attain this, we have created an adapter class MediaAdapter which implements the MediaPlayer interface and uses AdvancedMediaPlayer objects to play the required format.

AudioPlayer uses the adapter class MediaAdapter passing it the desired audio type without knowing the actual class which can play the desired format. AdapterPatternDemo, our demo class will use AudioPlayer class to play various formats.

Step 1

Create interfaces for Media Player and Advanced Media Player.

MediaPlayer.java

public interface MediaPlayer {
   public void play(String audioType, String fileName);
}

AdvancedMediaPlayer.java

public interface AdvancedMediaPlayer {	
   public void playVlc(String fileName);
   public void playMp4(String fileName);
}

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Step 2

Create concrete classes implementing the AdvancedMediaPlayer interface.

VlcPlayer.java

public class VlcPlayer implements AdvancedMediaPlayer{
   @Override
   public void playVlc(String fileName) {
  System.out.println("Playing vlc file. Name: "+ fileName);		   }

   @Override
   public void playMp4(String fileName) {
  //do nothing   }
}

Mp4Player.java

public class Mp4Player implements AdvancedMediaPlayer{

   @Override
   public void playVlc(String fileName) {
  //do nothing   }

   @Override
   public void playMp4(String fileName) {
  System.out.println("Playing mp4 file. Name: "+ fileName);		   }
}

Step 3

Create adapter class implementing the MediaPlayer interface.

MediaAdapter.java

public class MediaAdapter implements MediaPlayer {

   AdvancedMediaPlayer advancedMusicPlayer;

   public MediaAdapter(String audioType){
   
  if(audioType.equalsIgnoreCase("vlc") ){
     advancedMusicPlayer = new VlcPlayer();			
     
  }else if (audioType.equalsIgnoreCase("mp4")){
     advancedMusicPlayer = new Mp4Player();
  }	   }

   @Override
   public void play(String audioType, String fileName) {
   
  if(audioType.equalsIgnoreCase("vlc")){
     advancedMusicPlayer.playVlc(fileName);
  }
  else if(audioType.equalsIgnoreCase("mp4")){
     advancedMusicPlayer.playMp4(fileName);
  }   }
}

Step 4

Create concrete class implementing the MediaPlayer interface.

AudioPlayer.java

public class AudioPlayer implements MediaPlayer {
   MediaAdapter mediaAdapter; 

   @Override
   public void play(String audioType, String fileName) {		

  //inbuilt support to play mp3 music files
  if(audioType.equalsIgnoreCase("mp3")){
     System.out.println("Playing mp3 file. Name: " + fileName);			
  } 
  
  //mediaAdapter is providing support to play other file formats
  else if(audioType.equalsIgnoreCase("vlc") || audioType.equalsIgnoreCase("mp4")){
     mediaAdapter = new MediaAdapter(audioType);
     mediaAdapter.play(audioType, fileName);
  }
  
  else{
     System.out.println("Invalid media. " + audioType + " format not supported");
  }   }   
}

Step 5

Use the AudioPlayer to play different types of audio formats.

AdapterPatternDemo.java

public class AdapterPatternDemo {
   public static void main(String[] args) {
  AudioPlayer audioPlayer = new AudioPlayer();
  audioPlayer.play("mp3", "beyond the horizon.mp3");
  audioPlayer.play("mp4", "alone.mp4");
  audioPlayer.play("vlc", "far far away.vlc");
  audioPlayer.play("avi", "mind me.avi");   }
}

Step 6

Verify the output.

Playing mp3 file. Name: beyond the horizon.mp3
Playing mp4 file. Name: alone.mp4
Playing vlc file. Name: far far away.vlc
Invalid media. avi format not supported

August 31, 2024

Prototype Pattern

Prototype pattern refers to creating duplicate object while keeping performance in mind. This type of design pattern comes under creational pattern as this pattern provides one of the best ways to create an object.

This pattern involves implementing a prototype interface which tells to create a clone of the current object. This pattern is used when creation of object directly is costly. For example, an object is to be created after a costly database operation. We can cache the object, returns its clone on next request and update the database as and when needed thus reducing database calls.

Implementation

We’re going to create an abstract class Shape and concrete classes extending the Shape class. A class ShapeCache is defined as a next step which stores shape objects in a Hashtable and returns their clone when requested.

PrototypPatternDemo, our demo class will use ShapeCache class to get a Shape object.

Step 1

Create an abstract class implementing Clonable interface.

Shape.java

public abstract class Shape implements Cloneable {
   
   private String id;
   protected String type;
   
   abstract void draw();
   
   public String getType(){
  return type;   }
   
   public String getId() {
  return id;   }
   
   public void setId(String id) {
  this.id = id;   }
   
   public Object clone() {
  Object clone = null;
  
  try {
     clone = super.clone();
     
  } catch (CloneNotSupportedException e) {
     e.printStackTrace();
  }
  
  return clone;   }
}

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Step 2

Create concrete classes extending the above class.

Rectangle.java

public class Rectangle extends Shape {

   public Rectangle(){
 type = "Rectangle";   }

   @Override
   public void draw() {
  System.out.println("Inside Rectangle::draw() method.");   }
}

Square.java

public class Square extends Shape {

   public Square(){
 type = "Square";   }

   @Override
   public void draw() {
  System.out.println("Inside Square::draw() method.");   }
}

Circle.java

public class Circle extends Shape {

   public Circle(){
 type = "Circle";   }

   @Override
   public void draw() {
  System.out.println("Inside Circle::draw() method.");   }
}

Step 3

Create a class to get concrete classes from database and store them in a Hashtable.

ShapeCache.java

import java.util.Hashtable;

public class ShapeCache {
	
   private static Hashtable<String, Shape> shapeMap  = new Hashtable<String, Shape>();

   public static Shape getShape(String shapeId) {
  Shape cachedShape = shapeMap.get(shapeId);
  return (Shape) cachedShape.clone();   }

   // for each shape run database query and create shape
   // shapeMap.put(shapeKey, shape);
   // for example, we are adding three shapes
   
   public static void loadCache() {
  Circle circle = new Circle();
  circle.setId("1");
  shapeMap.put(circle.getId(),circle);
  Square square = new Square();
  square.setId("2");
  shapeMap.put(square.getId(),square);
  Rectangle rectangle = new Rectangle();
  rectangle.setId("3");
  shapeMap.put(rectangle.getId(), rectangle);   }
}

Step 4

PrototypePatternDemo uses ShapeCache class to get clones of shapes stored in a Hashtable.

PrototypePatternDemo.java

public class PrototypePatternDemo {
   public static void main(String[] args) {
  ShapeCache.loadCache();
  Shape clonedShape = (Shape) ShapeCache.getShape("1");
  System.out.println("Shape : " + clonedShape.getType());		
  Shape clonedShape2 = (Shape) ShapeCache.getShape("2");
  System.out.println("Shape : " + clonedShape2.getType());		
  Shape clonedShape3 = (Shape) ShapeCache.getShape("3");
  System.out.println("Shape : " + clonedShape3.getType());		   }
}

Step 5

Verify the output.

Shape : Circle
Shape : Square
Shape : Rectangle

August 31, 2024

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

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

Packing.java

public interface Packing {
   public String pack();
}

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Step 2

Create concrete classes implementing the Packing interface.

Wrapper.java

public class Wrapper implements Packing {

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

Bottle.java

public class Bottle implements Packing {

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

Step 3

Create abstract classes implementing the item interface providing default functionalities.

Burger.java

public abstract class Burger implements Item {

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

   @Override
   public abstract float price();
}

ColdDrink.java

public abstract class ColdDrink implements Item {

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

	@Override
	public abstract float price();
}

Step 4

Create concrete classes extending Burger and ColdDrink classes

VegBurger.java

public class VegBurger extends Burger {

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

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

ChickenBurger.java

public class ChickenBurger extends Burger {

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

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

Coke.java

public class Coke extends ColdDrink {

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

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

Pepsi.java

public class Pepsi extends ColdDrink {

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

   @Override
   public 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;

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());
  }		   }	
}

Step 6

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

MealBuilder.java

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;   }
}

Step 7

BuiderPatternDemo uses MealBuider to demonstrate builder pattern.

BuilderPatternDemo.java

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());   }
}

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

August 31, 2024