We have already discussed the functionality part of classes and objects, now we'll see the data part of it. Actually, they are nothing but ordinary variables which are bound to the classes and objects namespaces i.e. the names are valid within the context of these classes and objects only.
There are two types of fields - class variables and object variables which are classified depending on whether the class or the object owns the variables respectively.Class variables are shared in the sense that they are accessed by all objects (instances) of that class. There is only copy of the class variable and when any one object makes a change to a class variable, the change is reflected in all the other instances as well.
Object variables are owned by each individual object/instance of the class. In this case, each object has its own copy of the field i.e. they are not shared and are not related in any way to the field by the samen name in a different instance of the same class. An example will make this easy to understand.