Class And Object In Java

Object-Oriented Programming (OOP) is a programming model where programs are organized around objects and data rather than action and logic. OOP allows the decomposition of a problem into several entities called objects and then builds data and functions around these objects. Using the blueprint analogy, a class is a blueprint, and an object is a building made from that blueprint.

Let define a class: A class is the core of any modern Object-Oriented Programming language such as Java. In OOP languages it is mandatory to create a class for representing data. A class is a blueprint of an object that contains variables for storing data and functions to perform operations on the data. A class will not occupy any memory space and hence it is only a logical representation of data.


public class Circle {
   double radius;
   String color;
   
   double getRadius() {
   }

   double getArea() { 
   }
}

public class Circle {

double radius;

String color;

double getRadius() {

}

double getArea() {

}

Let define an object: Objects are the basic run-time entities of an object-oriented system. They may represent a person, a place, or any item that the program must handle. The software is divided into several small units which are an instance of a class called objects. An object is a software bundle of related variables and methods. The data of the objects can be accessed only by the functions associated with that object.


Circle c1, c2, c3;  // They hold a special value called null
// Construct the instances via new operator
c1 = new Circle();
c2 = new Circle(2.0);
c3 = new Circle(3.0, "red");
 
// You can Declare and Construct in the same statement
Circle c4 = new Circle();

Circle c1, c2, c3; // They hold a special value called null

// Construct the instances via new operator

c1 = new Circle();

c2 = new Circle(2.0);

c3 = new Circle(3.0, "red");

// You can Declare and Construct in the same statement

Circle c4 = new Circle();

Difference between object and class:

No.	Object	Class
1)	An object is an instance of a class.	Class is a blueprint or template from which objects are created.
2)	The object is a real-world entity such as a pen, laptop, mobile, bed, keyboard, mouse, chair, etc.	Class is a group of similar objects.
3)	The object is a physical entity.	The class is a logical entity.
4)	The object is created through a new keyword mainly e.g. Student s1=new Student();	Class is declared using class keyword e.g. class Student{}
5)	The object is created many times as per requirement.	The class is declared once.
6)	Object allocates memory when it is created.	Class doesn’t allocate memory when it is created.
7)	There are many ways to create objects in java such as new keyword, newInstance() method, clone() method, factory method, and deserialization.	There is only one way to define a class in java using the class keyword.

The article was published on August 8, 2017 @ 4:59 PM

Class And Object In Java

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