Class and Object in Java

Introductions of Class and Object:

Class:

• Class is used to hold data members and member function i.e. variables and functions.
• It can be easily accessed anywhere and used to reduce the reusability of the code.

For example,

• Let’s take student,
• Student properties are all called variables and student performance or student-related calculations(i.e. student result based on total and it may be pass or fail) is called as a function.

Where,

The student is a class.

Student properties (variables) : Roll_num,name,age,ect.

Student behaviours(function)  : total,average,result,fees details ect.

Note:

• If one or more variables declared within the class, called data members.
• If one or more functions declared within the class, called member function.

Object:

• An object is used to access the members of the class.
• It simply said as the short name of the class.

Syntax:

1. <import packages>
   Access_specifiers class class_name //class declaration
   {
             Variable_declaration;
             Method declaration or function_declaration()
             {
             //Statements
             }
   public static void main(String[] args)
   {
   //object declaration
   class_name obj_name new=class_name();
   //accessing member function using object
   obj_name.function_name();
   }
2. }

Note:

The class name and object name is a user-defined word.

Access specifiers:

• Java access specifiers are used for determining or setting the boundary for the availability of class members (data members and member functions) beyond that class.

Types of access specifiers:

• Private – It is used to access the data member and member function within the classes.
• Public – It is used to access the data member and member function out of the class. That means any class can be accessible.
• Protected – It members cannot be accessed from outside the class, however, they can be accessed in inherited classes.

Example:

1.  package oops_examples;

   import java.util.Scanner;

   public class Class_and_obj_Example_program {

       int sno, m1, m2, m3, m4, m5, tot;

       String name;

       float avg;

       void get()//Method for value get from user

       {

           Scanner sc = new Scanner(System.in);

           System.out.println("Enter student number : ");

           sno = sc.nextInt();

           System.out.println("Enter student name : ");

           name = sc.next();

           System.out.println("Enter Five subject mark : ");

           m1 = sc.nextInt();

           m2 = sc.nextInt();

           m3 = sc.nextInt();

           m4 = sc.nextInt();

           m5 = sc.nextInt();

       }

       void result()//Method for calculating total and average

       {

           tot = m1 + m2 + m3 + m4 + m5;

           avg = tot / 5;

       }

       void display()//Method for displaying full details

       {

           System.out.println("Student details............");

           System.out.println("Student id is : " + sno);

           System.out.println("Student name is : " + name);

           System.out.println("Five subject marks : \t" + m1 + "\t" + m2 + "\t" + m3 + "\t" + m4 + "\t" + m5);

           System.out.println("Total mark for five subject :" + tot);

           System.out.println("Average mark for five subject :" + avg);

       }

       public static void main(String[] args) {

           Class_and_obj_Example_program c = new Class_and_obj_Example_program();//object declaration

   //accessing member function using object

           c.get();

           c.result();

           c.display();

       }

   }

Output:

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