Java OOPs Concepts

In this page, we will learn about basics of OOPs. Object Oriented Programming is a paradigm that provides many concepts such as inheritance, data binding, polymorphism etc.

An object in OOP has some state and behavior. In Java, the state is the set of values of an object’s variables at any particular time and the behaviour of an object is implemented as methods.

OOPs (Object Oriented Programming System)

java oops concepts Object means a real word entity such as pen, chair, table etc. Object-Oriented Programming is a methodology or paradigm to design a program using classes and objects. It simplifies the software development and maintenance by providing some concepts:

• Object
• Class
• Inheritance
• Polymorphism
• Abstraction
• Encapsulation

Object

Any entity that has state and behavior is known as an object. For example: chair, pen, table, keyboard, bike etc. It can be physical and logical.

Class

Collection of objects is called class. It is a logical entity. Class can be considered as the blueprint or a template for an object and describes the properties and behavior of that object, but without any actual existence. An object is a particular instance of a class which has actual existence and there can be many objects (or instances) for a class.

Inheritance

When one object acquires all the properties and behaviours of parent object i.e. known as inheritance. It provides code reusability. It is used to achieve runtime polymorphism.

A class can get some of its characteristics from a parent class and then add more unique features of its own. For example, consider a Vehicle parent class and a child class Car. Vehicle class will have properties and functionalities common for all vehicles. Car will inherit those common properties from the Vehicle class and then add properties which are specific to a car.

In the above example, Vehicle parent class is known as base class or superclass. Car is known as derived class, Child class or subclass.

Java supports single-parent, multiple-children inheritance and multilevel inheritence (Grandparent-> Parent -> Child) for classes and interfces.

Java supports multiple inheritance (multiple parents, single child) only through interfaces. This is done to avoid some confusions and errors such as diamond problem of inheritance.

Polymorphism

When one task is performed by different ways i.e. known as polymorphism. For example: to convense the customer differently, to draw something e.g. shape or rectangle etc.

In java, we use method overloading and method overriding to achieve polymorphism.

Abstraction

Hiding internal details and showing functionality is known as abstraction. For example: phone call, we don’t know the internal processing.

In java, we use abstract class and interface to achieve abstraction.

Encapsulation

Binding (or wrapping) code and data together into a single unit is known as encapsulation. For example: capsule, it is wrapped with different medicines.

A java class is the example of encapsulation. Java bean is the fully encapsulated class because all the data members are private here.

Encapsulate in plain English means to enclose or be enclosed in or as if in a capsule. In Java, everything is enclosed within a class or interface, unlike languages such as C and C++ where we can have global variables outside classes.

Encapsulation enables data hiding, hiding irrelevant information from the users of a class and exposing only the relevant details required by the user. We can expose our operations hiding the details of what is needed to perform that operation.