A class is blueprint for creating objects. It defines the
structure and behavior. It can contain methods and variables while object
consists of a state and related behavior that is created from a class.
Difference between Object and Class
1. Object is an instance of a class while Class is
a blueprint from which objects are created.
2. Object is a real world entity such as table,
chair, phone ,etc while Class is a group of similar objects.
3) Object is a physical entity while Class is
a logical entity.
4) Object is created through new while Class is
created using class keyword.
5) Object is created many times as per requirement
while Class is declared once.
6) Object allocates memory when it is created while
Class doesn't allocated memory when it is created
Programming Example of Class and Object
//defining
or creating Payroll class
class Payroll {
int Empno; //data member or instance variables
String Empname; //data member or instance
variables
String empDept;//data member or instance
variables
String empPost;//data member or instance
variables
float empsalary; //data member or instance variables
//Creating
a method called dataentry
void dataentry(int no, String
name,String dept, String post, float sa) {
Empno=no;
Empname=name;
empDept=dept;
empPost=post;
empsalary=sa;
}
//Creating
a method called emprecord
void emprecord(){System.out.println(Empno+" "+Empname+" "+empDept+ " "+ empPost+ " "+empsalary);}
}
//Creating
another class Personnel with main method inside
public class Zap {
public static void main(String[] args) {
//Creating
an object of Payroll
Payroll record1=new Payroll();
Payroll record2=new Payroll();
Payroll record3=new Payroll();
Payroll record4=new Payroll();
System.out.println("==========================================");
System.out.println("Analysis of Payment ");
System.out.println("==========================================");
//accessing
member through reference variables or actual parameters
record1.dataentry(11,"Joe James ", "Sales ","Manager ", 18000);
record2.dataentry(12,"kyari Bello ","Production ","Accountant ",8000);
record3.dataentry(13,"Ahmed Bob ","Sales ","Clerk ",59000);
record4.dataentry(14,"Johnson AJAYI ","Sales ","Clerk ",8999);
record1.emprecord(); //Calling of the method
record2.emprecord();
record3.emprecord();
record4.emprecord();
}
}
Output
==========================================
Analysis
of Payment
==========================================
11 Joe
James Sales Manager 18000.0
12 kyari
Bello Production Accountant
8000.0
13 Ahmed
Bob Sales Clerk 59000.0
14 Johnson AJAYI Sales Clerk 8999.0
Explanation
From the above example Two Classes are defined. We have the
Payroll class and the Zap class.
In the Payroll class instance variables and two methods are
created. The instance variables in the Payroll class are :
Empname;
empDept;
empPost;
empsalary;
while the two methods are void
emprecord(){ } and void dataentry(list of parameters){}
The class from above
illustration contains methods and variables. The Keywords class is used to create
both the Payroll class and Zap class which is the main class.
The Payroll class uses in
creating the following objects in the main class . e.g
//Creating
an object of Payroll
Payroll record1=new Payroll();
Payroll record2=new Payroll();
Payroll record3=new Payroll();
Payroll record4=new Payroll();
We use Payroll in creating multiple objects in the above example and each of these objects has different name. e.g record1, record2, record3 and record4.
These objects are all instance of the
Payroll Class. new keyword is used in creating those objects. These
objects created are used in calling the
method of the class. i.e record1, record2,
record3 and record4.
For example.
record1.dataentry(11,"Joe James ", "Sales ","Manager ", 18000);
record2.dataentry(12,"kyari Bello ","Production ","Accountant ",8000);
record3.dataentry(13,"Ahmed Bob ","Sales ","Clerk ",59000);
record4.dataentry(14,"Johnson AJAYI ","Sales ","Clerk ",8999);
record1.emprecord(); //Calling of the method
record2.emprecord();
record3.emprecord();
record4.emprecord();
Reference
Eck, D. J. (2019). Introduction to programming using Java,
version 8.1. Hobart and William Smith College. http://math.hws.edu/javanotes
https://www.javatpoint.com/object-and-class-in-java
Gallardo, R., Hommel, S., Kannan, S., Gordon, J., and
Zakhour, S.B. (2016). The Java tutorials. Oracle.
What is an
object? https://docs.oracle.com/javase/tutorial/java/concepts/object.html