The document discusses various software design patterns including Singleton, MVC, Factory Method, and Observer. It provides examples of when and how each pattern is used. For instance, the Singleton pattern ensures only one instance of a resource exists, like a database connection. The MVC pattern separates business logic from presentation logic. The Factory Method creates object instances by defining an interface, while the Observer pattern allows objects to watch others for state changes. Design patterns provide proven solutions to common software problems and facilitate communication between designers.

1. Design Patterns Authors: Deepak Kumar & Swapnil Chandra

2. Design Patterns were introduced to the software community in ' Design Patterns ' by software architect Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides Colloquially known as the "gang of four" A Design Pattern is a known solution to commonly occurring problems or scenarios in software design. It is a kind of a template or structure on which one can code the application. What Are Design Patterns?

3. Common Software Design Patterns ... Singleton Pattern MVC (i.e. Model-View-Controler) Factory Method Observer

4. Singleton Pattern ... This pattern is used in applications when only a single instance of a resource is required Most common type of resource, on which this can be applied is database connection You want to share the database handle in an application because it's an overhead to keep opening and closing connections, particularly during a single page fetch An object is a singleton if the application can include one and only one of that object at a time

5. Model-View-Controller, this is the most commonly used design pattern This patterns separates the business logic and presentation logic in such a way that any changes in the presentation logic should not interfere with the business logic and vice-versa This is done with the help of a middle object called controller whose job is to take the request from the view pass it on the model if required present the updated/new view to the user. MVC Pattern ...

6. Factory Method is a object oriented creational pattern The method is used to create and initiate objects for classes Use of factories gives the programmer the opportunity to abstract the specific attributes of an Object into specific subclasses which create them i.e. it defines an interface for creating an object, but let the subclasses decide which class to instantiate. Factory Pattern ...

7. Observer pattern allows one object (the observer) to watch another (the subject) The subject object notify the observer object if the subject’s state changes (Conceptually, the Observer pattern in something like a trigger in a database, which runs a stored procedure when a table row is modified The main advantage of this pattern is that it decouples the observer from the subject The subject doesn’t need to know anything special about its observers. Instead, the subject simply allows observers to subscribe. Observer Pattern ...

8. Design patterns have two major benefits. First, they provide you with a way to solve issues related to software development using a proven solution. The solution facilitates the development of highly cohesive modules with minimal coupling Second, design patterns make communication between designers more efficient. Software professionals can immediately picture the high-level design in their heads when they refer the name of the pattern used to solve a particular issue when discussing system design. Benefits of Design Patterns ...

9. Conclusion ... There are many other reational/structural/ behavioral patterns, like Iterator, Adapter, Prototype, State etc. But in order to implement a pattern effectively a detailed study is done at our end here at Mobicules Systems to understand the nature of the problem and how a particular design pattern solves it.

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