Design Patterns
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The document discusses design patterns, including definitions, types of patterns, and examples. It explains the Model-View-Controller (MVC) pattern, how it separates an application into the model, view, and controller components. It also covers the Singleton pattern, which ensures only one instance of a class can be created and provides a global access point. The Singleton pattern has early and lazy instantiation forms. The document provides examples of implementing these patterns in code.
![Definitions of Design Patterns
Design patterns are recurring solutions to design problems you see
over & over [smaltalk Companion]
Design patterns constitute a set of rules describing how to
accomplish certain tasks in the realm of software development
[Pree,1994]
Design patterns focus more on reuse of recurring architectural
design themes, while frameworks focus on detailed design &
implementation[Coplien & Schmid ,1995]
3](https://image.slidesharecdn.com/presentation1-151028185354-lva1-app6891/85/Design-Patterns-3-320.jpg)
![Definitions of Design Patterns
A pattern addresses a recurring design problem that arise in
specific design situations & presents a solution to it [Buschmann et
al.,1996]
Patterns identify & specify abstractions that are above the level of
single classes and instances, or of components.[Gammar et
al.,1993]
4](https://image.slidesharecdn.com/presentation1-151028185354-lva1-app6891/85/Design-Patterns-4-320.jpg)
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Design Patterns
- 2. Content Definitions of Design Patterns Model-View-Controller Design Pattern Types Singleton Design Pattern 2
- 3. Definitions of Design Patterns Design patterns are recurring solutions to design problems you see over & over [smaltalk Companion] Design patterns constitute a set of rules describing how to accomplish certain tasks in the realm of software development [Pree,1994] Design patterns focus more on reuse of recurring architectural design themes, while frameworks focus on detailed design & implementation[Coplien & Schmid ,1995] 3
- 4. Definitions of Design Patterns A pattern addresses a recurring design problem that arise in specific design situations & presents a solution to it [Buschmann et al.,1996] Patterns identify & specify abstractions that are above the level of single classes and instances, or of components.[Gammar et al.,1993] 4
- 5. Model-View-Controller The Model-View-Controller (MVC) pattern is one of the earliest and one of the most successful design patterns. It was developed by Trygve Reenskaug in 1979. Controller Data Model View 5
- 6. Model-View-Controller Data Model : Contains the computation part of the program View : Which presents the user interface Controller : Which interacts between the user & the view 6
- 7. Model-View-Controller Employee Object as a Model EmployeeView a Class which display Employee Information as a View EmployeeControl a Class which controls the data flow into model object and updates the view whenever data changes - Controller. 7
- 8. Model-View-Controller Interaction It helps to separate the applications concerns EmployeeController EmployeeModel EmployeeView Sees Uses ManipulateUpdate 8
- 9. Data Model Data ,methods for accessing and modifying state A model stores data that is retrieved according to commands from the controller and displayed in the view 9
- 10. Data Model Object of this class can use to hold the data & methods 10
- 11. View When model changed view must update A view generates an output presentation to the user based on changes in the model 11
- 12. View Present Information in Console Window 12
- 13. Controller Translate user actions into operations on the model. Act as a separator between Model & View. A controller can send commands to the Model to update the model's state (e.g., editing a document) Associated view to change the view's presentation of the model (e.g., by scrolling through a document). 13
- 14. Controller 14
- 15. Test Class 15
- 16. Design Pattern Types Creational Patterns Structural Patterns Behavioral Patterns 16
- 17. Creational Patterns Deals with object creation Control the object creation Trying to create objects in a manner suitable to the situation 17
- 18. Creational Patterns 1. Abstract Factory 2. Builder 3. Factory Method 4. Object Pool 5. Prototype 6. Singleton 18
- 19. Singleton Pattern Define a class that has only one instance(class must ensure that only single instance should be created) Provides a global point of access to it(single object can be used by all other classes) Is a class of which there may be no more than one instance. It provides single global point of access to that instance 19
- 20. Singleton Pattern When to Use When its important to have only one instance of a class Only a print spooler One window manager One point of access to database engine Among several serial ports only one instance of COM1 Centralized management of internal or external resources and they provide a global point of access to themselves Singleton pattern is mostly used in multi-threaded and database applications. 20
- 21. Forms of Singleton Pattern Singleton Pattern Early Instantiation (Load Time instance creation) Lazy Instantiation (Create instance when required) 21
- 22. Singleton Pattern - Advantages Reuse single instance save memory 22
- 23. Singleton Pattern UML <<public class >> 23
- 24. Singleton Pattern Class Static member Store the instance of the class Get memory only once as it is static Private constructor Prevent creating instances outside the class Static factory method (Static factory method is simply a static method that returns an instance of a class.) Provides the global point of access to the Singleton object Returns the instance to the caller. 24
- 25. Singleton Pattern Early Instantiation Create the instance of the class at the time of class loading 25
- 26. Singleton Pattern lazy Instantiation Create the instance of the class in synchronized method or synchronized block Instance of the class is created when required 26
- 27. Singleton Pattern lazy Instantiation 27
- 28. Conclusion MVC Pattern stands for Model-View-Controller Pattern. This pattern is used to separate application's concerns. Singleton Pattern Is a class of which there may be no more than one instance. It provides single global point of access to that instance 28
- 29. References https://sourcemaking.com/design_patterns/creational_patterns http://www.oodesign.com/singleton-pattern.html#early-singleton http://www.javatpoint.com/core-java-design-patterns Java Design Patterns James W.Cooper 29
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