ClassVariableInJava.txt

--class variables in Java--

Class Variables are an important concept in java programming. This  Class variables also known as static variables are declared 
with the static keyword in a class, but outside a method, constructor or a block. There would only be one copy of each class 
variable per class, regardless of how many objects are created from it.

--Important Terminology--
When a number of objects are created from the same class blueprint, they each have their own distinct copies of instance variables. 
In the case of the 'Car' class, the instance variables are cadence, gear, and speed. 
Each 'car' object has its own values for these variables, stored in different memory locations.

variables that are common to all objects is gained by the static modifier.
Fields that have the static modifier in their declaration are called static fields or class variables. 



For example, suppose you want to create a number of 'Car' objects and assign each a serial number, beginning with 1 for the first object. This ID number is unique to each object and is therefore an instance variable. At the same time, you need a field to keep track of how many Bicycle objects have been created so that you know what ID to assign to the next one. Such a field is not related to any individual object, but to the class as a whole. For this you need a class variable, numberOfBicycles, as follows:


Example Syntax
public class Car {
        
    private int cadence;
    private int gear;
    private int speed;
        
    // add an instance variable for the object ID
    private int id;
    
    // add a class variable for the
    // number of Car objects instantiated
    private static int numberOfCars = 0;
        ...
}


Class variables are referenced by the class name itself, as in

Car.numberOfBicycles