Java Object and Class

In Java, An object is a physical as well as a logical entity. Whereas a class in Java is only a logical entity. Classes are used to create and manage objects and help to support inheritance.

An object is a collection of related data/functionality. Objects are created to share some behaviour. Objects can be created to call non-static methods which are not presented inside the Main Method but present inside the class.

Object

An object is the building block of the object-oriented programming language. An object is a real-world entity with its own attributes, behaviour and identity.

Real World Examples for objects

Characteristics of object

An object has three characteristics:

• STATE: It represents the data or value of an object.
• BEHAVIOUR: It represents the functionality or methods of an object.
• IDENTITY: Each object has a unique identity. Each object is uniquely identifiable.

Example of an Object

How to initialise the object in the class

Objects can be initialised in three ways.

Class

In Java, A class is a fundamental building block of Object-oriented programming(OOP) language. A class can define the structure, behaviour and state of an Object.

A class can be defined in two ways :

• Class expression.
• Class declaration.

How to declare a class in Java

We can declare a class using the “class” keyword in front of the class name, followed by the curly braces.

Class declaration

Public class Dataflair{
// body of the class(field and method)
}

Create a class

Create a class named ‘DataFlair” with String S
    public class DataFlair {
     		int x =6;
     	  In this example, we will create a class named with “DataFlair”

Create an object

  Create an object called “obj” and print the value of S
public class DataFlair {
        int x = 6;
        public static void main(String[] args) {
            DataFlair obj = new DataFlair();
        System.out.println(obj.x);
    }
}

Output:

6

In the above program, we have created a class named “DataFlair,” which contains a variable x. Inside a class, we have created an object named “obj”, and then we use the objects to call the methods of a class.

Multiple objects

We can create more than one object in one class. For example:

class DataFlair{
Int x = 6;
int y = 8;
String s = “Data Flair”;
Public static void main(String args[])
{
DataFlair obj1 = new DataFlair();
DataFlair obj2 = new DataFlair();
DataFlair obj3 = new DataFlair();
System.out.println(obj1.x);
System.out.println(obj2.y);
System.out.println(obj3.s);
}
}

Output :

6
8
Data Flair

In the above program, we have created a class named “DataFlair.” it contains 3 variables: x, y and s. Inside a class, we have created an object named “obj1”, “obj2”, and “obj3.” Then, we used the objects to call the methods of a class.

Difference between classes and object

CLASS	OBJECT
A template for creating objects within a program.	An instance of a class.
Logical entity.	Physical entity.
Declared with the “class” keyword.	Created using the “new” keyword
A class is declared once.	Multiple objects are created using a class.
A class does not have memory when it is created.	Objects get memory when they are created.