# OO Design Principles

### SOLID Principle:

* SOLID is a mnemonic acronym for five different OOD principles intended to make software design more understandable, flexible and maintainable.
* Combining this five principles, it makes easy for the programmer to develop a software that are easy to maintain and extend.
* It makes easy to avoid code smells and easy code refractor.

**S - Single-responsibility**

A class should have one and only one reason to change, states that a class should have only one job.

**O - Open-Closed**

Objects or entities should be open for extend and closed for modification. It means that, class should be easily extendable instead of modifying the class directly.

**L - Liskov Substitution**

It states that every subclasses/derived classes should be substitutable for their base/parent class.

**I - Interface Segregation**

A client should never be forced to implement an interface that it doesn't use or clients shouldn't be forced to depend on methods they do not use.

**EX:** Creating a single interface for multiple objects, create different interfaces based on their requirements.

**D - Dependency Inversion**

Entities must depend on abstractions not on concretions. It states that the high level module must not depend on the low level module, but they should depend on abstractions.

### DRY Principle:

* DRY - Don't repeat yourself is a software development principle aimed at reducing the repetition of software patterns. It is replaceable, to avoid redundancy with abstraction or using data normalization.
* This principle is stated as Every piece of knowledge must have a single, clear-cut, authoritative responsibility within a system.
*  When the DRY principle is applied successfully, a modification of any single element of a system does not require a change in other logically unrelated elements. Additionally, elements that are logically related all change predictably and uniformly, and are thus kept in sync.

### Other principles:

**KISS** -  "Keep it simple, silly", "keep it short and simple", "keep it simple and straightforward", "keep it small and simple", or "keep it stupid simple".

 **GRASP -** General Responsibility Assignment Software Patterns.

 **IDEF4 -** Integrated DEFinition for Object-Oriented Design - design of component-based client/server systems.


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