Object Oriented Principals in plain language

Keep it simple

If you know how to write code in a Object Oriented language, you probably know how to implement its primitive concepts, you know how to declare a method as private or how to subclass from a class. But can we explain what Polymorphism is in plain English? Or what if during an interview you are asked about Abstraction, what do you say? Here is a simple reasonable explanation of each in case you are asked in an interview:

Inheritance:

Inheritance allows us to subclass from a class. In object oriented programming classes are all members of hierarchy classes and that is possible with Inheritance principle.
Child class inherits methods and properties form the parent. This enables the developers to reuse the code easily.

Abstraction: 

Abstraction means representing essential features without including implementations. What does that mean? Abstraction is a concept or paradigm of describing things in simpler terms (abstract details) depending on its location in inheritance hierarchy. It helps representing essential features without being worried about the implementation. At the most abstract level there is no implementation details. More abstract concepts are at the top and more concrete ideas go to the bottom. This graph represent a general idea of abstraction concept:

Interface is a set of methods with no implementations. Abstract classes contain both abstract and concrete methods and they must be inherited.

Encapsulation:

Encapsulation is used to define, hide and restrict properties and methods outside access. It prevents unnecessary access to methods and properties (class is container encapsulating the data). The access is available only if required, this handles by access modifiers:

• Public: Accessible from everywhere
• Protected: Accessible within the same package and subclasses
• Default (no specifier): Accessible form inside the package
• Private: Only accessible within the same class, not visible to subclasses

		Public	Protected	Default	Private
	Class	✔️	✔️	✔️	✔️
	Package	✔️	✔️	✔️	❌
	Subclass(Same Package)	✔️	✔️	✔️	❌
	Subclass(Different Package)	✔️	✔️	❌	❌
	World	✔️	❌	❌	❌

Polymorphism:

Polymorphism give us availability to define a method (in subclass) that is already declared in the parent class. Generally there are two types of polymorphism: 

• Compile time polymorphism or overloading:
  You can define several methods with the same name, the only difference will be the method signatures.
• Run time polymorphism or overriding: 
  You can define methods with the same name and signature as parent class (or the implemented interface). This gives us ability to define the methods that is specific to particular subclass. 

If you have OOP keyword on your resume, you should be able to explain these concepts but not limited to these four.