Object Oriented Programming concepts in JAVA

Object Oriented
Programming
concepts

Concept
• Definition: Class is a blue print (Abstraction)
• Class defines
– State (Characteristics/Attributes)
– Behaviour
Java
• The basic unit of object-orientation in Java is Class.
Class – basis of all computation
State
Behaviour

Concept
• Have specific identity (Not a
blueprint)
• Have specific attributes (state)
and behavior.
Java
• Instance of a class
Objects
State
Behaviour

public class Car
{
/* Attributes that define the state of the class are declared here*/
/* These variables are called instance variables (or) member variables */
public String make;
public String model;
public String colour;
public float mileage;
public float distance;
/*Methods that define the behavior of the class are declared here*/
Class in Java
State
public class Car
Class: Car
Member variables (or)
Instance variables
Member methods
Access
Modifier
Keyword
Class name
(identifier)

//Methods that define the behavior of the class are declared here. Only these methods can access the
instance //variables or instance variables.
public void setMileage(){
//Code to set the current mileage of the car
}
public void chgDistance(){
//Code to update the distance travelled so far
}
public void dispDetails(){
//Code to view the details of the car
}
} // End of Class
Class in Java (Code continues…)
Behaviour

public static void main(){
Car c2 = new Car(“BMW”,”x3”,”Alphine-White”,15,0);
Car c3 = new Car(“Ferrari”,” GTC4Lusso”,”Giallo Modena”,4,0);
}
Objects in Java
Car c1 = new Car( “Hyuindai”,”Creta”,”Typhoon-silver”, 19,0 );
Class name
Object name
‘new’ - keyword for creating objects
Constructor - method to initialize an object
Parameters for constructor objects
Constructor
It is a special type of method in the
name of the class that initializes the
object.
Car
c1 c2 c3
We will discuss this
later(1)

Class and its objects
C1
Brand: Hyuindai
Model: Creta
Colour: Typhoon-Silver
Mileage: 19
Distance covered: 0
C2
Brand: BMW
Model: X3
Colour: Alphine-white
Mileage: 15
Distance covered: 0
C3
Brand: Ferrari
Model: GTC4Lusso
Colour: Giallo Modena
Mileage: 4
Distance covered: 0
Class: Car

Terms used in Object Oriented
Programming (OOP)
• Data encapsulation
Ability to combine state & behavior (member
variables and member methods) is called data
encapsulation.
• Data abstraction
Act of representing essential features without
including the background details or explanation.
(Generalization or Blue print)
Class: Car
Instance variables
Member methods

Programming (OOP)
• Class
Class is a blueprint of a set of objects that have
common structure and behavior.
• Object
An entity with specific identity, specific
characteristics and specific behavior.
An instance of a class.
Class: Car
Instance variables
Member methods

Programming (OOP)
• Polymorphism
Ability to take ‘many forms’ of the same
method.
• Inheritance
Derive part or all of the information from one
entity to another entity
later
later

 Special methods in Java that are called when an object is created.
 Used to initialize the objects.
 Name of the method is same as that of the class
 No explicit return type specified.
 There are two types
 Default constructor (Called when no constructor is defined in the class)
 Parameterized constructor
Constructor methods in Java

Constructor methods in Java
public class Car
{
//declare instance variables here
//define member methods here
Car (String mke, String mdl, String clr, float mile, float dist){
make= mke;
model= mdl;
colour= clr;
mileage= mile;
distance= dist;
}
Car (String mke, String mdl, String clr){
make= mke;
model= mdl;
colour= clr;
mileage= 0;
distance= 0;
}
}
public static void main(){
Car c1 = new Car(); //default constructor
Car c2 = new Car(“BMW”,”x3”,”Alphine-
White”,15,0); //Parameterized constructor-1
Car c3 = new Car(“Ferrari”,” GTC4Lusso”,”Giallo
Modena”); //Parameterized constructor-2
}
Polymorphism –
Three constructor
functions with
same name.

Levels of access
Public
Accessible to any other
class anywhere
Protected
Accessible to package
classes and any
subclasses that are in
packages
Default
Accessible to classes in
the same package
Private
Accessible only within
the class
Package-1
Class-1
Class-2
Class-3
Package-2
Class-A
extends
Class-1
Class-B
Class-C
• Class level
• Package level
• Other package
– Subclass level
• Other package
– Non subclass
level
public void setMileage()
public void chgDistance()
Access modifier
• private
• default*
• protected
• public
*default is not a
keyword

 OOP concepts
 Data encapsulation (or) Data hiding
 Data abstraction
 Polymorphism
 Inheritance
Things to remember

 Class is a blueprint of objects.
 Object is an instance of class.
 Member variables (or) instance variables in a class
 Member methods in a class
 Constructor methods
 Creating objects
Things to remember

Object Oriented Programming concepts in JAVA

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