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--- softwaredesignpattern [2014/06/19 11:17] – [Design] admin
+++ softwaredesignpattern [2022/10/29 16:15] (current) – external edit 127.0.0.1
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+Refer: http://www.tutorialspoint.com/design_pattern/design_pattern_overview.htm
+====== Software Design Pattern ======
+**Design patterns** represent the best practices **used by experienced object-oriented software developers**. Design patterns are **solutions to general problems that software developers faced during software development**. These solutions were obtained by trial and error by numerous software developers over quite a substantial period of time.
+**Types of Desing Pattern**:As per the design pattern reference book Design Patterns - Elements of Reusable Object-Oriented Software , there are 23 design patterns. These patterns can be classified in three categories: Creational, Structural and behavioral patterns
+^S.N.^Name^Pattern & Description^
+|1|**Creational Patterns**|These design patterns provides **way to create objects while hiding the creation logic**, rather than instantiating objects directly using new opreator. This gives program more flexibility in deciding which objects need to be created for a given use case.|
+|2|**Structural Patterns**|These design patterns concern class and object composition. Concept of inheritance is used to compose interfaces and **define ways to compose objects to obtain new functionalities**.|
+|3|**Behavioral Patterns**|These design patterns are specifically **concerned with communication between objects**.|
+|4|**J2EE Patterns**|These design patterns are specifically **concerned with the presentation tier**. These patterns are identified by Sun Java Center.|
+===== Creational Pattern: Factory Pattern =====
+Factory pattern is one of most used design pattern in Java. This type of design pattern comes under creational pattern as **this pattern provides one of the best ways to create an object**.
+==== Design ====
+{{:other:factory_pattern_uml_diagram.jpg|}}
+==== Implementation ====
+  - Step 1: Create an interface **Shape.java**:<code java>
+public interface Shape {
+   void draw();
+}
+</code>
+  - Step 2: Create **concrete classes** implementing the same interface.
+    * Rectangle.java<code java>
+public class Rectangle implements Shape {
+   @Override
+   public void draw() {
+      System.out.println("Inside Rectangle::draw() method.");
+   }
+}
+</code>
+    * Square.java<code java>
+public class Square implements Shape {
+   @Override
+   public void draw() {
+      System.out.println("Inside Square::draw() method.");
+   }
+}
+</code>
+    * Circle.java<code java>
+public class Circle implements Shape {
+   @Override
+   public void draw() {
+      System.out.println("Inside Circle::draw() method.");
+   }
+}
+</code>
+  - Step 3: Create a Factory to generate object of concrete class based on given information **ShapeFactory.java**<code java>
+public class ShapeFactory {
+   //use getShape method to get object of type shape
+   public Shape getShape(String shapeType){
+      if(shapeType == null){
+         return null;
+      }
+      if(shapeType.equalsIgnoreCase("CIRCLE")){
+         return new Circle();
+      } else if(shapeType.equalsIgnoreCase("RECTANGLE")){
+         return new Rectangle();
+      } else if(shapeType.equalsIgnoreCase("SQUARE")){
+         return new Square();
+      }
+      return null;
+   }
+}
+</code>
+  - Step 4: Use the Factory to get object of concrete class by passing an information such as type FactoryPatternDemo.java:<code java>
+public class FactoryPatternDemo {
+   public static void main(String[] args) {
+      ShapeFactory shapeFactory = new ShapeFactory();
+      //get an object of Circle and call its draw method.
+      Shape shape1 = shapeFactory.getShape("CIRCLE");
+      //call draw method of Circle
+      shape1.draw();
+      //get an object of Rectangle and call its draw method.
+      Shape shape2 = shapeFactory.getShape("RECTANGLE");
+      //call draw method of Rectangle
+      shape2.draw();
+      //get an object of Square and call its draw method.
+      Shape shape3 = shapeFactory.getShape("SQUARE");
+      //call draw method of circle
+      shape3.draw();
+   }
+}
+</code>
+  - Step 5: Verify the output.<code>
+Inside Circle::draw() method.
+Inside Rectangle::draw() method.
+Inside Square::draw() method.
+</code>
+===== creational pattern: Singleton Pattern =====
+This class provides a way to access its only object which can be accessed directly without need to instantiate the object of the class.Ensure a class has only one instance, and provide a global point of access to it
+==== Design ====
+We're going to **create a SingleObject class**. SingleObject class have its constructor as private and **have a static instance of itself**.
+SingleObject class provides a static method to get its static instance to outside world. SingletonPatternDemo, our demo class will use SingleObject class to get a SingleObject object.
+{{:other:singleton_pattern_uml_diagram.jpg|}}
+==== Implementation ====
+  - Step 1: Create a Singleton Class SingleObject.java<code java>
+public class SingleObject {
+   //create an object of SingleObject
+   private static SingleObject instance = new SingleObject();
+   //make the constructor private so that this class cannot be
+   //instantiated
+   private SingleObject(){}
+   //Get the only object available
+   public static SingleObject getInstance(){
+      return instance;
+   }
+   public void showMessage(){
+      System.out.println("Hello World!");
+   }
+}
+</code>
+  - Step 2: Get the only object from the singleton class SingletonPatternDemo.java<code java>
+public class SingletonPatternDemo {
+   public static void main(String[] args) {
+      //illegal construct
+      //Compile Time Error: The constructor SingleObject() is not visible
+      //SingleObject object = new SingleObject();
+      //Get the only object available
+      SingleObject object = SingleObject.getInstance();
+      //show the message
+      object.showMessage();
+   }
+}
+</code>
+  - Step 3: Verify the output<code>
+Hello World!
+</code>
+===== Structural Pattern: 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.
+==== Design ====
+We've an interface **MediaPlayer interface** and a concrete class AudioPlayer implementing the MediaPlayer interface. AudioPlayer can **play mp3 format** audio files by default.
+We're having another interface **AdvancedMediaPlayer interface** 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've **created an adapter class MediaAdapter** which implements the MediaPlayer interface and uses AdvancedMediaPlayer objects to play the required format.\\
+{{:other:adapter_pattern_uml_diagram.jpg|}}\\
+{{:other:patternadapter.png|}}
+==== Implementation ====
+  - Step 1: **Create interfaces** for Media Player and Advanced Media Player
+    * MediaPlayer.java<code java>
+public interface MediaPlayer {
+   public void play(String audioType, String fileName);
+}
+</code>
+    * AdvancedMediaPlayer.java<code java>
+public interface AdvancedMediaPlayer {
+   public void playVlc(String fileName);
+   public void playMp4(String fileName);
+}
+</code>
+  - Step 2: Create **concrete classes** implementing the AdvancedMediaPlayer interface
+    * VlcPlayer.java<code 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
+   }
+}
+</code>
+    * Mp4Player.java<code 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);
+   }
+}
+</code>
+  - Step 3: Create **adapter class** implementing the MediaPlayer interface MediaAdapter.java<code 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);
+      }
+   }
+}
+</code>
+  - Step 4: Create **concrete class implementing the MediaPlayer interface** AudioPlayer.java<code 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");
+      }
+   }
+}
+</code>
+  - Step 5: Use the AudioPlayer to **play different types of audio formats** AdapterPatternDemo.java<code 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");
+   }
+}
+</code>
+  - Step 6: Verify the output<code>
+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
+</code>
+===== Structural Pattern: Composite Pattern =====
+Composite pattern is used where we need to treat a group of objects in similar way as a single object.
+==== Design ====
+We've 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.
+{{:other:composite_pattern_uml_diagram.jpg|}}
+==== Implementation ====
+  - Step 1: Create Employee class having list of Employee objects Employee.java<code 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<Employee>();
+   }
+   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 :[ Name : "+ name
+      +", dept : "+ dept + ", salary :"
+      + salary+" ]");
+   }
+}
+</code>
+  - Step 2: Use the Employee class to create and print employee hierarchy CompositePatternDemo.java<code 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);
+         }
+      }
+   }
+}
+</code>
+  - Step 3: Verify the output<code>
+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 ]
+</code>
+===== Structural Pattern: Decorator pattern =====
+Decorator pattern allows to **add new functionality 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**.
+==== Design ====
+Below are demonstrating use of Decorator pattern via following example in which we'll **decorate a shape** with **some color without alter shape class**.
+We're going to create a **Shape interface** and concrete classes implementing the Shape interface. We then create a 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.\\
+{{:other:decorator_pattern_uml_diagram.jpg|}}\\
+{{:other:patterndecorator.png|}}
+==== Implementation ====
+  - Step 1: Create an **interface Shape.java**<code java>
+public interface Shape {
+   void draw();
+}
+</code>
+  - Step 2: Create concrete classes implementing the same interface:
+    * Rectangle.java<code java>
+public class Rectangle implements Shape {
+   @Override
+   public void draw() {
+      System.out.println("Shape: Rectangle");
+   }
+}
+</code>
+    * Circle.java<code java>
+public class Circle implements Shape {
+   @Override
+   public void draw() {
+      System.out.println("Shape: Circle");
+   }
+}
+</code>
+  - Step 3: Create **abstract decorator class** implementing the Shape interface **ShapeDecorator.java**<code java>
+public abstract class ShapeDecorator implements Shape {
+   protected Shape decoratedShape;
+   public ShapeDecorator(Shape decoratedShape){
+      this.decoratedShape = decoratedShape;
+   }
+   public void draw(){
+      decoratedShape.draw();
+   }
+}
+</code>
+  - Step 4: Create concrete decorator class **extending the ShapeDecorator class RedShapeDecorator.java**<code 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");
+   }
+}
+</code>
+  - Step 5: Use the **RedShapeDecorator** to **decorate Shape objects** DecoratorPatternDemo.java<code 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();
+   }
+}
+</code>
+  - Step 6: Verify the output<code>
+Circle with normal border
+Shape: Circle
+Circle of red border
+Shape: Circle
+Border Color: Red
+Rectangle of red border
+Shape: Rectangle
+Border Color: Red
+</code>
+===== Behavior Pattern: Iterator Pattern =====
+Iterator pattern is very commonly used design pattern in Java and .Net programming environment. This pattern is used to **get a way to access the elements of a collection object** in sequential manner **without any need to know its underlying representation**.
+==== Design ====
+{{:other:iterator_pattern_uml_diagram.jpg|}}\\
+{{:other:iteratorpattern.png|}}
+==== Implementation ====
+  - Step 1: Create interfaces:
+    * Iterator.java<code java>
+public interface Iterator {
+   public boolean hasNext();
+   public Object next();
+}
+</code>
+    * Container.java<code java>
+public interface Container {
+   public Iterator getIterator();
+}
+</code>
+  - Step 2: Create concrete class implementing the Container interface. This class has inner class NameIterator implementing the Iterator interface NameRepository.java<code java>
+public class NameRepository implements Container {
+   public String names[] = {"Robert" , "John" ,"Julie" , "Lora"};
+   @Override
+   public Iterator getIterator() {
+      return new NameIterator();
+   }
+   private class NameIterator implements Iterator {
+      int index;
+      @Override
+      public boolean hasNext() {
+         if(index < names.length){
+            return true;
+         }
+         return false;
+      }
+      @Override
+      public Object next() {
+         if(this.hasNext()){
+            return names[index++];
+         }
+         return null;
+      }
+   }
+}
+</code>
+  - Step 3: Use the NameRepository to get iterator and print names IteratorPatternDemo.java<code java>
+public class IteratorPatternDemo {
+   public static void main(String[] args) {
+      NameRepository namesRepository = new NameRepository();
+      for(Iterator iter = namesRepository.getIterator(); iter.hasNext();){
+         String name = (String)iter.next();
+         System.out.println("Name : " + name);
+      }
+   }
+}
+</code>
+  - Step 4: Verify the output<code>
+Name : Robert
+Name : John
+Name : Julie
+Name : Lora
+</code>
+===== Behavior Pattern: Observer Pattern =====
+Observer pattern is used when there is one to many relationship between objects such as **if one object is modified, its depenedent objects are to be notified automatically**. Observer pattern falls under behavioral pattern category.
+==== Design ====
+Observer pattern uses three actor classes. **Subject, Observer and Client**. **Subject, an object having methods to attach and de-attach observers to a client object**. We've created classes Subject, Observer abstract class and concrete classes extending the abstract class the Observer.
+ObserverPatternDemo, our demo class will use Subject and concrete class objects to show observer pattern in action.\\
+{{:other:observer_pattern_uml_diagram.jpg|}}\\
+{{:other:patternobserver.png|}}
+==== Implementation ====
+  - Step 1: Create **Subject class** Subject.java:<code java>
+import java.util.ArrayList;
+import java.util.List;
+public class Subject {
+   private List<Observer> observers
+      = new ArrayList<Observer>();
+   private int state;
+   public int getState() {
+      return state;
+   }
+   public void setState(int state) {
+      this.state = state;
+      notifyAllObservers();
+   }
+   public void attach(Observer observer){
+      observers.add(observer);
+   }
+   public void notifyAllObservers(){
+      for (Observer observer : observers) {
+         observer.update();
+      }
+   }
+}
+</code>
+  - Step 2: Create Observer class Observer.java<code java>
+public abstract class Observer {
+   protected Subject subject;
+   public abstract void update();
+}
+</code>
+  - Step 3: Create concrete observer classes:
+    * BinaryObserver.java<code java>
+public class BinaryObserver extends Observer{
+   public BinaryObserver(Subject subject){
+      this.subject = subject;
+      this.subject.attach(this);
+   }
+   @Override
+   public void update() {
+      System.out.println( "Binary String: "
+      + Integer.toBinaryString( subject.getState() ) );
+   }
+}
+</code>
+    * OctalObserver.java<code java>
+public class OctalObserver extends Observer{
+   public OctalObserver(Subject subject){
+      this.subject = subject;
+      this.subject.attach(this);
+   }
+   @Override
+   public void update() {
+     System.out.println( "Octal String: "
+     + Integer.toOctalString( subject.getState() ) );
+   }
+}
+</code>
+    * HexaObserver.java<code java>
+public class HexaObserver extends Observer{
+   public HexaObserver(Subject subject){
+      this.subject = subject;
+      this.subject.attach(this);
+   }
+   @Override
+   public void update() {
+      System.out.println( "Hex String: "
+      + Integer.toHexString( subject.getState() ).toUpperCase() );
+   }
+}
+</code>
+  - Step 4: Use Subject and concrete observer objects ObserverPatternDemo.java<code java>
+public class ObserverPatternDemo {
+   public static void main(String[] args) {
+      Subject subject = new Subject();
+      new HexaObserver(subject);
+      new OctalObserver(subject);
+      new BinaryObserver(subject);
+      System.out.println("First state change: 15");
+      subject.setState(15);
+      System.out.println("Second state change: 10");
+      subject.setState(10);
+   }
+}
+</code>
+  - Step 5: Verify the output<code>
+First state change: 15
+Hex String: F
+Octal String: 17
+Binary String: 1111
+Second state change: 10
+Hex String: A
+Octal String: 12
+Binary String: 1010
+</code>
+===== Behavior Pattern:State Pattern =====
+In State pattern a **class behavior changes based on its state**. This type of design pattern comes under behavior pattern.
+==== Design ====
+We're going to create a **State interface defining a action** and **concrete state classes implementing the State interface**. Context is a class which carries a State.
+StatePatternDemo, our demo class will use Context and **state objects to demonstrate change in Context behavior based on type of state** it is in.\\
+{{:other:state_pattern_uml_diagram.jpg|}}\\
+{{:other:patternstate.png|}}
+==== Implementation ====
+  - Step 1: Create an interface Image.java<code java>
+public interface State {
+   public void doAction(Context context);
+}
+</code>
+  - Step 2: Create concrete classes implementing the same interface
+    * StartState.java<code java>
+public class StartState implements State {
+   public void doAction(Context context) {
+      System.out.println("Player is in start state");
+      context.setState(this);
+   }
+   public String toString(){
+      return "Start State";
+   }
+}
+</code>
+    * StopState.java<code java>
+public class StopState implements State {
+   public void doAction(Context context) {
+      System.out.println("Player is in stop state");
+      context.setState(this);
+   }
+   public String toString(){
+      return "Stop State";
+   }
+}
+</code>
+  - Step 3: Create Context Class Context.java<code java>
+public class Context {
+   private State state;
+   public Context(){
+      state = null;
+   }
+   public void setState(State state){
+      this.state = state;
+   }
+   public State getState(){
+      return state;
+   }
+}
+</code>
+  - Step 4: Use the Context to see change in behaviour when State changes StatePatternDemo.java<code java>
+public class StatePatternDemo {
+   public static void main(String[] args) {
+      Context context = new Context();
+      StartState startState = new StartState();
+      startState.doAction(context);
+      System.out.println(context.getState().toString());
+      StopState stopState = new StopState();
+      stopState.doAction(context);
+      System.out.println(context.getState().toString());
+   }
+}
+</code>
+  - Step 5: Verify the output<code>
+Player is in start state
+Start State
+Player is in stop state
+Stop State
+</code>
+===== Model-View-Controller Pattern =====
+This pattern is used to separate application's concerns:
+  * Model - Model **represents an object** or JAVA POJO carrying data. It can **also have logic to update controller if its data changes**.
+  * View - View **represents the visualization of the data** that model contains.
+  * Controller - Controller acts on both Model and view. It **controls the data flow into model object** and **updates the view whenever data changes**. It keeps **View and Model separate**.
+==== Design ====
+We're going to create a **Student object** acting as a model. **StudentView** will be a view class which can print student details on console and **StudentController** is the controller class responsible to store data in Student object and update view StudentView accordingly.
+**MVCPatternDemo**, our demo class will use StudentController to **demonstrate use of MVC pattern**.\\
+{{:other:mvc_pattern_uml_diagram.jpg|}}\\
+{{:other:patternmvc.png|}}
+==== Implementation ====
+  - Step 1: Create Model Student.java<code java>
+public class Student {
+   private String rollNo;
+   private String name;
+   public String getRollNo() {
+      return rollNo;
+   }
+   public void setRollNo(String rollNo) {
+      this.rollNo = rollNo;
+   }
+   public String getName() {
+      return name;
+   }
+   public void setName(String name) {
+      this.name = name;
+   }
+}
+</code>
+  - Step 2: Create View StudentView.java<code java>
+public class StudentView {
+   public void printStudentDetails(String studentName, String studentRollNo){
+      System.out.println("Student: ");
+      System.out.println("Name: " + studentName);
+      System.out.println("Roll No: " + studentRollNo);
+   }
+}
+</code>
+  - Step 3: Create Controller StudentController.java<code java>
+public class StudentController {
+   private Student model;
+   private StudentView view;
+   public StudentController(Student model, StudentView view){
+      this.model = model;
+      this.view = view;
+   }
+   public void setStudentName(String name){
+      model.setName(name);
+   }
+   public String getStudentName(){
+      return model.getName();
+   }
+   public void setStudentRollNo(String rollNo){
+      model.setRollNo(rollNo);
+   }
+   public String getStudentRollNo(){
+      return model.getRollNo();
+   }
+   public void updateView(){
+      view.printStudentDetails(model.getName(), model.getRollNo());
+   }
+}
+</code>
+  - Step 4: Use the StudentController methods to demonstrate MVC design pattern usage MVCPatternDemo.java<code java>
+public class MVCPatternDemo {
+   public static void main(String[] args) {
+      //fetch student record based on his roll no from the database
+      Student model  = retriveStudentFromDatabase();
+      //Create a view : to write student details on console
+      StudentView view = new StudentView();
+      StudentController controller = new StudentController(model, view);
+      controller.updateView();
+      //update model data
+      controller.setStudentName("John");
+      controller.updateView();
+   }
+   private static Student retriveStudentFromDatabase(){
+      Student student = new Student();
+      student.setName("Robert");
+      student.setRollNo("10");
+      return student;
+   }
+}
+</code>
+  - Step 5: Verify the output<code>
+Student:
+Name: Robert
+Roll No: 10
+Student:
+Name: John
+Roll No: 10
+</code>
+===== Behavior Pattern:Command Pattern =====
+==== Design ====
+We've created an **interface Order** which is **acting as a command**. We've created a **Stock class** which acts **as a request**. We've concrete command classes **BuyStock and SellStock implementing Order interface** which will do **actual command processing**. A class **Broker** is created which acts **as a invoker object**. It can take order and place orders.
+Broker object uses command pattern to identify which object will execute which command based on type of command. CommandPatternDemo, our demo class will use Broker class to demonstrate command pattern.
+{{:other:command_pattern_uml_diagram.jpg|}}\\
+{{:other:patterncommand.png|}}
+==== Implementation ====
+  - Step 1: Create a command interface Order.java<code java>
+public interface Order {
+   void execute();
+}
+</code>
+  - Step 2: Create a request class Stock.java<code java>
+public class Stock {
+   private String name = "ABC";
+   private int quantity = 10;
+   public void buy(){
+      System.out.println("Stock [ Name: "+name+",
+         Quantity: " + quantity +" ] bought");
+   }
+   public void sell(){
+      System.out.println("Stock [ Name: "+name+",
+         Quantity: " + quantity +" ] sold");
+   }
+}
+</code>
+  - Step 3: Create concrete classes implementing the Order interface:
+    * BuyStock.java<code java>
+public class BuyStock implements Order {
+   private Stock abcStock;
+   public BuyStock(Stock abcStock){
+      this.abcStock = abcStock;
+   }
+   public void execute() {
+      abcStock.buy();
+   }
+}
+</code>
+    * SellStock.java<code java>
+public class SellStock implements Order {
+   private Stock abcStock;
+   public SellStock(Stock abcStock){
+      this.abcStock = abcStock;
+   }
+   public void execute() {
+      abcStock.sell();
+   }
+}
+</code>
+  - Step 4: Create command invoker class Broker.java<code java>
+import java.util.ArrayList;
+import java.util.List;
+   public class Broker {
+   private List<Order> orderList = new ArrayList<Order>();
+   public void takeOrder(Order order){
+      orderList.add(order);
+   }
+   public void placeOrders(){
+      for (Order order : orderList) {
+         order.execute();
+      }
+      orderList.clear();
+   }
+}
+</code>
+  - Step 5: Use the Broker class to take and execute commands CommandPatternDemo.java<code java>
+public class CommandPatternDemo {
+   public static void main(String[] args) {
+      Stock abcStock = new Stock();
+      BuyStock buyStockOrder = new BuyStock(abcStock);
+      SellStock sellStockOrder = new SellStock(abcStock);
+      Broker broker = new Broker();
+      broker.takeOrder(buyStockOrder);
+      broker.takeOrder(sellStockOrder);
+      broker.placeOrders();
+   }
+}
+</code>
+  - Step 6: Verify the output<code>
+Stock [ Name: ABC, Quantity: 10 ] bought
+Stock [ Name: ABC, Quantity: 10 ] sold
+</code>
+===== Behavior Pattern: Template Pattern =====
+Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.
+==== Design ====
+{{:other:template_pattern_uml_diagram.jpg|}}\\
+{{:other:patterntemplate.png|}}\\
+==== Implementation ====
+  - Step 1: Create an abstract class with a template method being final Game.java<code java>
+public abstract class Game {
+   abstract void initialize();
+   abstract void startPlay();
+   abstract void endPlay();
+   //template method
+   public final void play(){
+      //initialize the game
+      initialize();
+      //start game
+      startPlay();
+      //end game
+      endPlay();
+   }
+}
+</code>
+  - Step 2: Create concrete classes extending the above class
+    * Cricket.java<code java>
+public class Cricket extends Game {
+   @Override
+   void endPlay() {
+      System.out.println("Cricket Game Finished!");
+   }
+   @Override
+   void initialize() {
+      System.out.println("Cricket Game Initialized! Start playing.");
+   }
+   @Override
+   void startPlay() {
+      System.out.println("Cricket Game Started. Enjoy the game!");
+   }
+}
+    * Football.java<code java>
+public class Football extends Game {
+   @Override
+   void endPlay() {
+      System.out.println("Football Game Finished!");
+   }
+   @Override
+   void initialize() {
+      System.out.println("Football Game Initialized! Start playing.");
+   }
+   @Override
+   void startPlay() {
+      System.out.println("Football Game Started. Enjoy the game!");
+   }
+}
+</code>
+  - Step 3: Use the Game's template method play() to demonstrate a defined way of playing game TemplatePatternDemo.java<code java>
+public class TemplatePatternDemo {
+   public static void main(String[] args) {
+      Game game = new Cricket();
+      game.play();
+      System.out.println();
+      game = new Football();
+      game.play();
+   }
+}
+</code>
+  - Step 4: Verify the output<code>
+Cricket Game Initialized! Start playing.
+Cricket Game Started. Enjoy the game!
+Cricket Game Finished!
+Football Game Initialized! Start playing.
+Football Game Started. Enjoy the game!
+Football Game Finished!
+</code>