Objects Oriented Concepts in java programming.

Object Oriented Concepts:

Class: In Java, a class is a definition of objects of the same kind. In other words, a class is a blueprint, template, or prototype that defines and describes the static attributes and dynamic behaviors common to all objects of the same kind.

     A class can be visualized as a three-compartment box, as illustrated:

1.   Name (or identity): identifies the class.

2.   Variables (or attribute, state, field): contains the static attributes of the class.

3.   Methods (or behaviors, function, operation): contains the dynamic behaviors of the class.

 A class can contain any of the following variable types.

·        Local variables: Variables defined inside methods, constructors or blocks are called local variables. The variable will be declared and initialized within the method and the variable will be destroyed when the method has completed.

·        Instance variables: Instance variables are variables within a class but outside any method. These variables are initialized when the class is instantiated. Instance variables can be accessed from inside any method, constructor or blocks of that particular class.

·        Class variables: Class variables are variables declared with in a class, outside any method, with the static keyword.

     class Bicycle {

    int cadence = 0;

    int speed = 0;

    int gear = 1;

    void changeCadence(int newValue) {

         cadence = newValue;

    }

    void changeGear(int newValue) {

         gear = newValue;

    }

    void speedUp(int increment) {

         speed = speed + increment;  

    }

    void applyBrakes(int decrement) {

         speed = speed - decrement;

    }

    void printStates() {

         System.out.println("cadence:" +

             cadence + " speed:" +

             speed + " gear:" + gear);

    }

}

Object: Object is an instance of class. An instance is a realization of a particular item of a class.

   To create an instance of a class, you have to:

1.   Declare an instance identifier (instance name) of a particular class.

2.   Construct the instance (i.e., allocate storage for the instance and initialize the instance) using the "new" operator.

 Bicycle b;  // Declaration

 b= new Bicycle();  //Instantiation