Chapter -2 What is Class and Objects in Java

 Class and Objects in Java 

Click :---Java Object in Hindi

Click:---Java Class in Hindi

Introduction to java class and Object 

Class and Objects important parts of oops.

Look at the following Example represent through diagram.

Class	Objects
Fruits	Apple
	Banana
	Mango
	Papaya

 

Same As Another Example :-

Class	Objects
Students	Shailesh
	Annu
	Smriti
	Kajal

Class

Class :- It is an user defined data type, it is a template that defined properties and behaviours of objects and it is a real-life instance with blue print of any objects.

It is collections of similar type of objects, for Example:- Birds, Students, Fruits, Cars, Peoples, Animals etc..

Summary :-

• It is a collection of data members and member functions.
• Data members are the variable used inside class.
• Member functions are the function used inside class.
• It is also called Userdefined data type.

Object

Object :- Object is a real world entity.

In another world:- Objects is an entity that has state and behaviours. Here Now:-  State means:- Data and Behaviors means functionality.

Main Points :- Well Objects is an instance of a class, All the members of the class can be access through objects.

For example :- Parrot, Shailesh, Mango, Maruti etc.

• Object is having states and behaviors in which state means what does it has and behavior means what does it do. for example a pen has
• States:ink,nib,needle,cap etc
• Behaviors:Writing.

Impotent point to remember while making class program

⇒Declare variable with appropriate data type as per your requirement

for example to find the area of recatngle three variable are sufficient(height, width and area)

⇒Declare function as per your requirement

for example to find the area of recatngle single function findArea() is sufficient.

⇒Create instance(object) of class to access the data member and member function of a class.

classname objectname;

Example:- Rectangle rec1;

Here Rectangle is the name of class and rec1 is the name of object.

⇒Accessing data member and member fucntion

Data member and member fucntion of a class can be accessed using Dot(.) operator.

⇒Accessing data member

rec1.height;

⇒Accessing member function

rec1.findArea();

Example :- 

// Example 1: Find area of Rectangle but passing value in main fuctions

class Rectangle{

    int height;

    int width;

    int area;

    void findarea(){

        area = height* width;

        System.out.print("Area of rectangle:"+area);

    }

    public static void main(String args[]){

        Rectangle obj =new Rectangle(); // creatig Object

        obj.height=15;   // Passing value

        obj.width=10;

        obj.findarea(); // Access member function

    }

}

Example 2:- 

// Example 2: Find area of Rectangle using double member function

class Rect{

    // Passing Data member

    int h;

    int w;

    int area;

    // passing member function

    void getvalue(){

        h=19;

        w=15;

    }

    //  member function

    void findarea(){

        area = h*w;

        System.out.print("Area of Rectangle :-"+area);

    }

    public static void main(String args[]){

        Rect ra= new Rect(); // Creating obj

        ra.getvalue();

        ra.findarea();

    }

}

I hope this point is helpful 

Java Object in Hindi

Java Class in Hindi