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Unformatted text preview: an object and a
subprogram call. In the former case, the object executes the appropriate method with its own local data, whereas in the latter case the data to be processed is
usually sent along with the subprogram call to the subprogram code unit.
A class is a description of one or more similar objects. The class concept is similar
to "type" in the conventional procedure-oriented languages. For example, if
"integer" is a type (class), then "8" is an instance (object) of type (class) "integer".
Similarly, "Person-1" and "Person-2" can be two instances (objects) of a class
Multiple instances of a class can be created which are known as the objects of the
class. Each object has its own local data and represents a different instance of its
class. Since all the objects of a class share the same methods, the only difference
between two objects of the same class is the state of their local variables. Also
note that there can be two categories of object variables - class variables and
instance variables. Class variables are variables stored in the class whose values
are shared by all instances (objects) of the class. Instance variables are variables
for which local storage is available in the instances (objects).
Object-oriented programming languages also support class hierarchies. Subclasses of a given class are refinements of it, inheriting the functionality and local
variables of the parent-class, or super-class. Sub-classes can add new local
variables and methods and can modify or hide inherited methods.
In OOP, inheritance is a mechanism for sharing code and behavior. It allows a
programmer to reuse the behavior of a class in the definition of new classes. We
saw above that a program written in an object-oriented language may have a large
hierarchy of classes. In fact, good programming in an object-oriented language
depends, to a large extent, in creating sub-classes of existing classes because this
leads to potential reuse...
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This document was uploaded on 04/07/2014.
- Spring '14