Classes and Objects

Class :

          Class is the blue print of the real objects to be created. The class gives the skeleton for an entity to be created for real time processing. Class is a software template that defines the methods and variables to be included in a particular kind of Object.

A class may contain member variables, methods, constructors and static blocks which can be used to define and manupulate state and behavious of an object.

Object :

           The java is all about objects. An Object is the real entity in the world. Every object will have its state and behavior. Concept of Object can be easily understood taking any really time entity around us say Dog, television, Fridge or car etc.  A car may have states like number of wheels, type of engine etc and behvior like way of start, speedup etc.

Below is the syntax for the class.

Access specifier Class ClassName

{

                Member variables --- defines state of an object

                Methods --- defines the behaviour of the object

}

Object declaration will be like below:

ClassName object = new ClassName()

Example:

        We can define a class Vehicle to have an skeleton for all types of vehicles by preparing set of properties and type of processes required to use those vehicle. After that we can create real time object such as car, truck or tempo depending upon the states(properties).

Declaring a class : Vehicle

public class Vehicle

{

            //member variables which will define the state of a vehicle

private int wheels;

            private String sengineType;

            //setter method to set number of wheels

public void setWheels(int wheels)

{

                this.wheels = wheels;

}

//getter method to retrieve the number of wheels

public int getWheels()

{

                return this.wheels;

}             

}

See below, how will we use this class to instantiate any real object.

public class Demo

{

            //main method

            Public static void main(String args[])

{

            //calling default constructor to create an object.

Vehicle car = new Vehicle();       

Vehicle tempo = new Vehicle();

//calling setter method to set the states of the car object

            car.setWheels(4);

            tempo.setWheels(3);

            //calling getter method to access the object states

            System.out.println(“ Car : No. of wheels :”+car.getWheels());

System.out.println(“ Tempo : No. of wheels :”+tempo.getWheels());

}

}

.