OOP stands for Object-Oriented Programming. OOP is a programming paradigm in which every program is follows the concept of object. In other words, OOP is a way of writing programs based on the object concept.

The object-oriented programming paradigm has the following core concepts.

• Encapsulation
• Inheritance
• Polymorphism
• Abstraction

The popular object-oriented programming languages are Smalltalk, C++, Java, PHP, C#, Python, etc.

Encapsulation

Encapsulation is the process of combining data and code into a single unit (object / class). In OOP, every object is associated with its data and code. In programming, data is defined as variables and code is defined as methods. The java programming language uses the class concept to implement encapsulation.

Inheritance

Inheritance is the process of acquiring properties and behaviors from one object to another object or one class to another class. In inheritance, we derive a new class from the existing class. Here, the new class acquires the properties and behaviors from the existing class. In the inheritance concept, the class which provides properties is called as parent class and the class which recieves the properties is called as child class. The parent class is also known as base class or supre class. The child class is also known as derived class or sub class.

In the inheritance, the properties and behaviors of base class extended to its derived class, but the base class never receive properties or behaviors from its derived class.

In java programming language the keyword extends is used to implement inheritance.

Polymorphism

Polymorphism is the process of defining same method with different implementation. That means creating multiple methods with different behaviors.

The java uses method overloading and method overriding to implement polymorphism.

Method overloading - multiple methods with same name but different parameters.

Method overriding - multiple methods with same name and same parameters.

Abstraction

Abstraction is hiding the internal details and showing only esential functionality. In the abstraction concept, we do not show the actual implemention to the end user, instead we provide only esential things. For example, if we want to drive a car, we does not need to know about the internal functionality like how wheel system works? how brake system works? how music system works? etc.