What do you mean by Design Pattern? Why is it necessary? What are the common design patterns?

Design patterns are the generic solution to common object oriented software design. When solving any software design, we come across several issues that have common solutions. Design pattern can be useful at this step.

Why Design Pattern?

• It can speed up the development process by providing tested and proven software development paradigm.
• Improves code reusability
• Pattern allows developers to communicate using well known, well understood names of software interactions. 

Some of the common design patterns are as follows:

1. Creational Design pattern: These are concerned with creation of instances of one or more classes.  Some of its common types are factory method, abstract factory method, prototype, singleton, builder method, etc
2. Structural Method: These are concerned with objects and class composition. Some of the common structural  methods are adapter, bridge, composite, decorator, facade etc. 
3. Behavioral Design Pattern: These are concerned with class and objects communication and how objects communicates with one another. Some of common approaches of behavioral methods of design patterns are chain of responsibilities, command etc.