Classes and Objects

Classes and Objects:

-          A class is an user defined datatype which consists of methods and memberVariables.

-          An object consists of the data and the code that acts up on the data.

Ex:

                Class Emp  {

                                int empno;                                          //member variable

                                String ename;                                    //member variable

                                float salary;                                         //member variable

                               

                                public String getEname() {             //method

                                                return ename;

                                }

                                …

}

To access methods or memberVariables we need instances, like

                Emp emp1 = new Emp();

                emp1.getEname();

-          In simple language,

Class is a blueprint of an Object, Object is an instance of a class.

-          In OOPs, the fundamental data storage is an Object. i.e..

-          Hence,

A class is a conceptual part of a program ,

An object is the physical representation of a class.

-          Any object must possess the following characteristics:

o    State

§  It represents the data.

§  It is indicated by attributes , values for these attributes.

o    Behavior

§  It represents the methods.

§  It refers to the change of the state over a period of time.

o    Identity

§  It represents the name of the object.

§  Each object must have an unique identity.