Design pattern allows us to reuse the experience or rather, provides reusable solutions to commonly occurring problems. 

Design Pattern Introduction
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• A design pattern is a general reusable solution to a commonly occurring problem within a given context in software design. 
• design pattern is not a finished design that can be transformed directly into source or machine code. 
•It is a description or template for how to solve a problem that can be used in many different situations. 
•Patterns are formalized best practices that the programmer must implement in the application. Object-oriented design patterns typically show relationships and interactions between classes or objects, without specifying the final application classes or objects that are involved. Patterns that imply object-orientation or more generally mutable state, are not as applicable in functional programming languages.

The types of design patterns are Creational, Structural, and Behavioral design patterns.


Creational design patterns are design patterns that deal with object creation mechanisms, trying to create objects in a manner suitable to the situation. The basic form of object creation could result in design problems or added complexity to the design. Creational design patterns solve this problem by somehow controlling this object creation. Types of creational design patterns are:

    •Singleton Pattern
    •Factory Pattern
    •Abstract Factory Pattern
    •Builder Pattern
    •Prototype Pattern
    
    

Structural design patterns are design patterns that ease the design by identifying a simple way to realize relationships between entities.

    •Adapter Pattern
    •Composite Pattern
    •Proxy Pattern
    •Flyweight Pattern
    •Facade Pattern
    •Bridge Pattern
    •Decorator Pattern

Behavioral design patterns are design patterns that identify common communication patterns between objects and realize these patterns. By doing so, these patterns increase flexibility in carrying out this communication.

    •Template Method Pattern
    •Mediator Pattern
    •Chain of Responsibility Pattern
   •Observer Pattern
    •Strategy Pattern
    •Command Pattern
    •State Pattern
    •Visitor Pattern
    •Iterator Pattern
    •Memento Pattern