The document discusses object-oriented programming (OOP) concepts in Java, focusing on the definition and characteristics of objects and classes. It explains that objects are instances of classes, which define the attributes and methods applicable to those objects. Additionally, examples illustrate how to implement classes and create object instances in Java.

1. Objects and Classes in JAVA

2. OO Programming Concepts
• Object-oriented programming (OOP) involves
programming using objects.
• An object represents an entity in the real
world.
• For example, a student, a desk, a circle, a
button can all be viewed as objects.

3. • Objects will have state and behavior
• The state of an object (also known as its
properties or attributes) is represented by
data fields with their current values.
• EG: A rectangle object has the data fields
width and height, which are the properties
that characterize a rectangle

4. • The behavior of an object (also known as its
actions) is defined by methods.
• To invoke a method on an object is to ask the
object to perform an action.
• For example, you may define methods named
getArea() and getPerimeter() for circle
objects.

5. An object is an instance of a class.
You can create many instances of a class.
Creating an instance is referred to as
instantiation.

6. Classes
• Classes are constructs that define objects of
the same type.

7. • A class defines a kind of objects:
– specifies the kinds of attributes (data) an
object of the class can have.
– provides methods specifying the actions an
object of the class can take.
• An object is an instance of the class.
• Person is a class
– Alice and Bob are objects of the Person class.

8. What does a class have?
• Members of a class:
– Attributes (instance variables, data)
• For each instance of the class (object),
values of attributes can vary, hence
instance variables
– Methods
• Person class
– Attributes: name, address, phone number
– Methods: change address, change phone
number

9. Example class
Class student {
int id;
String name;
Public static void main(String args[])
{
student s1=new student();
System.out.println(s1.id);
System.out.println(s1.name);
}
}

10. Class student {
int id;
String name;
}
Class test1
{
public static void main(String args[])
{
student s1=new student();
S1.id=100;
S1.name=“abc”;
System.out.println(“s1.id+ “ “+s1.name+” “);
}
}

11. Class student {
Int rollno;
String name;
Void read(int r,String n)
{ rollno=r;
name=n;
}
Void display()
{
System.out.println(rollno+” “+name);
}
}
Class student1 {
public static void main(String args[])
{
student s1=new student();
Student s2=new student();
S1.read(100,”Karan”);
S2.read(200,”Aryan”);
S1.display();
S2.display()
}