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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();
}
}
Step5
Verify the output.
Inside Circle::draw() method.
Inside Rectangle::draw() method.
Inside Square::draw() method.](https://image.slidesharecdn.com/designpatterntutorial-180919110853/85/Design-pattern-tutorial-12-320.jpg)
Design pattern tutorial
- 2. i AbouttheTutorial 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. This tutorial will take you through step by step approach and examples using Java while learning Design Pattern concepts. Audience This reference has been prepared for the experienced developers to provide best solutions to certain problems faced during software development and for un- experienced developers to learn software design in an easy and faster way. Prerequisites Before you start proceeding with this tutorial, we make an assumption that you are already aware of the basic concepts of Java programming. Copyright&Disclaimer Copyright 2015 by Tutorials Point (I) Pvt. Ltd. All the content and graphics published in this e-book are the property of Tutorials Point (I) Pvt. Ltd. The user of this e-book is prohibited to reuse, retain, copy, distribute or republish any contents or a part of contents of this e-book in any manner without written consent of the publisher. We strive to update the contents of our website and tutorials as timely and as precisely as possible, however, the contents may contain inaccuracies or errors. Tutorials Point (I) Pvt. Ltd. provides no guarantee regarding the accuracy, timeliness or completeness of our website or its contents including this tutorial. If you discover any errors on our website or in this tutorial, please notify us at contact@tutorialspoint.com
- 3. ii TableofContents About the Tutorial....................................................................................................................................i Audience..................................................................................................................................................i Prerequisites............................................................................................................................................i Copyright & Disclaimer.............................................................................................................................i Table of Contents....................................................................................................................................ii 1. DESIGN PATTERN OVERVIEW ..............................................................................................1 What is Gang of Four (GOF)?...................................................................................................................1 Usage of Design Pattern..........................................................................................................................1 Types of Design Patterns.........................................................................................................................1 2. FACTORY PATTERN..............................................................................................................3 Implementation ......................................................................................................................................3 3. ABSTRACT FACTORY PATTERN.............................................................................................7 Implementation ......................................................................................................................................7 4. SINGLETON PATTERN ........................................................................................................15 Implementation ....................................................................................................................................15 5. BUILDER PATTERN.............................................................................................................18 Implementation ....................................................................................................................................18 6. PROTOTYPE PATTERN........................................................................................................26 Implementation ....................................................................................................................................26 7. ADAPTER PATTERN............................................................................................................32 Implementation ....................................................................................................................................32 8. BRIDGE PATTERN...............................................................................................................38 Implementation ....................................................................................................................................38
- 4. iii 9. FILTER PATTERN ................................................................................................................42 Implementation ....................................................................................................................................42 10. COMPOSITE PATTERN .......................................................................................................50 Implementation ....................................................................................................................................50 11. DECORATOR PATTERN.......................................................................................................54 Implementation ....................................................................................................................................54 12. FACADE PATTERN..............................................................................................................59 Implementation ....................................................................................................................................59 13. FLYWEIGHT PATTERN........................................................................................................63 Implementation ....................................................................................................................................63 14. PROXY PATTERN................................................................................................................69 Implementation ....................................................................................................................................69 15. CHAIN OF RESPONSIBILITY PATTERN .................................................................................72 Implementation ....................................................................................................................................72 16. COMMAND PATTERN ........................................................................................................77 Implementation ....................................................................................................................................77 17. INTERPRETER PATTERN .....................................................................................................81 Implementation ....................................................................................................................................81 18. ITERATOR PATTERN...........................................................................................................85 Implementation ....................................................................................................................................85 19. MEDIATOR PATTERN .........................................................................................................88 Implementation ....................................................................................................................................88 20. MEMENTO PATTERN.........................................................................................................91 Implementation ....................................................................................................................................91
- 5. iv 21. OBSERVER PATTERN..........................................................................................................95 Implementation ....................................................................................................................................95 22. STATE PATTERN...............................................................................................................100 Implementation ..................................................................................................................................100 23. NULL OBJECT PATTERN....................................................................................................104 Implementation ..................................................................................................................................104 24. STRATEGY PATTERN ........................................................................................................108 Implementation ..................................................................................................................................108 25. TEMPLATE PATTERN........................................................................................................112 Implementation ..................................................................................................................................112 26. VISITOR PATTERN............................................................................................................116 Implementation ..................................................................................................................................116 27. MVC PATTERN.................................................................................................................121 Implementation ..................................................................................................................................121 28. BUSINESS DELEGATE PATTERN........................................................................................126 Implementation ..................................................................................................................................126 29. COMPOSITE ENTITY PATTERN..........................................................................................131 Implementation ..................................................................................................................................131 30. DATA ACCESS OBJECT PATTERN ......................................................................................136 Implementation ..................................................................................................................................136 31. FRONT CONTROLLER PATTERN........................................................................................141 Implementation ..................................................................................................................................141 32. INTERCEPTNG FILTER PATTERN.......................................................................................145 Implementation ..................................................................................................................................145
- 6. v 33. SERVICE LOCATOR PATTERN............................................................................................151 Implementation ..................................................................................................................................151 34. TRANSFER OBJECT PATTERN............................................................................................157 Implementation ..................................................................................................................................157
- 7. 6 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. WhatisGangofFour(GOF)? In 1994, four authors Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides published a book titled Design Patterns - Elements of Reusable Object- Oriented Software which initiated the concept of Design Pattern in Software development. These authors are collectively known as Gang of Four (GOF). According to these authors design patterns are primarily based on the following principles of object orientated design. Program to an interface not an implementation Favor object composition over inheritance UsageofDesignPattern Design Patterns have two main usages in software development. Commonplatformfordevelopers Design patterns provide a standard terminology and are specific to particular scenario. For example, a singleton design pattern signifies the use of single object so all developers familiar with single design pattern will make use of single object and they can tell each other that program is following a singleton pattern. BestPractices Design patterns have been evolved over a long period of time and they provide best solutions to certain problems faced during software development. Learning these patterns help unexperienced developers to learn software design in an easy and fast way. DESIGN PATTERN OVERVIEW
- 8. 7 TypesofDesignPatterns As per the design pattern reference book Design Patterns - Elements of Reusable Object-Oriented Software, there are 23 design patterns which can be classified in three categories: Creational, Structural and Behavioral patterns. We will also discuss another category of design pattern: J2EE design patterns. S.N. Pattern & Description 1 Creational Patterns These design patterns provide a way to create objects while hiding the creation logic, rather than instantiating objects directly using new operator. This gives more flexibility to the program 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.
- 9. 8 Factory pattern is one of most used design patterns in Java. This type of design pattern comes under creational pattern as this pattern provides one of the best ways to create an object. In Factory pattern, we create objects without exposing the creation logic to the client and refer to newly created object using a common interface. Implementation We are going to create a Shape interface and concrete classes implementing the Shape interface. A factory class ShapeFactory is defined as a next step. FactoryPatternDemo, our demo class, will use ShapeFactory to get a Shape object. It will pass information (CIRCLE / RECTANGLE / SQUARE) to ShapeFactory to get the type of object it needs. Step1 Create an interface. Shape.java FACTORY PATTERN
- 10. 9 public interface Shape { void draw(); } Step2 Create concrete classes implementing the same interface. Rectangle.java public class Rectangle implements Shape { @Override public void draw() { System.out.println("Inside Rectangle::draw() method."); } } Square.java public class Square implements Shape { @Override public void draw() { System.out.println("Inside Square::draw() method."); } } Circle.java public class Circle implements Shape { @Override public void draw() { System.out.println("Inside Circle::draw() method."); }
- 11. 10 } Step3 Create a Factory to generate object of concrete class based on given information. ShapeFactory.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; } } Step4 Use the Factory to get object of concrete class by passing an information such as type. FactoryPatternDemo.java public class FactoryPatternDemo {
- 12. 11 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(); } } Step5 Verify the output. Inside Circle::draw() method. Inside Rectangle::draw() method. Inside Square::draw() method.
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