Object Oriented Programming - Java Programming Course - Chapter 2
Object Oriented
Programming
Object:
·
The object oriented programming involves programming
by using objects.
·
An object represents an entity in the real world that
can be distinctly identified.
Ex: student,fan,light,circle,etc.,
·
An object has unique identity: State and behavior
·
State: The state
of an object is nothing but the properties or attributes of the object which
are represented by data fields or members.
Ex: The circle object has data fields like radius
, area ,perimeter etc.,
·
Behavior: The behavior
of an object is nothing but the actions what we want to do on the object. The
behavior is represented by methods. Ex: Calculate Area(),Calculate Perimeter().
Class :
·
A class is a template blueprint which represents the
state & behavior of objects.
·
Program to create a class Circle with radius &
methods calArea() & calPerimeter().
class Circle
{
double radius; //here radius is called data field
double calArea()
//calArea() is a method
{
double area;
area=radius*radius*Math.PI;
return area;
}
double calPerimeter()
{
Double per;
per=2*Math.PI*radius;
return per;
}
}
Inorder to access the data fields and methods in the program we have to
create instances of the class which means creating an object.
Syntax for creating object:
classname objectname=new classname();
new is an operator used to create
objects.
Creating object for above example:
Circle c1=new Circle();
So, this will be the continuation of above program(writing main() method
and creating object):
class MyCircle
{
public static void main(String
args[])
{
Circle c1=new Circle();
c1.radius=13;
double a=c1.calArea();
double p=c1.calPerimeter();
System.out.println(“Area of
circle= “+a+”Perimeter of circle =” +p);
}
}
So the output will be:
Area of circle= 531.1428571429
Perimeter of circle = 81.7142857143
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