Polymorphism :

Polymorphism is another important OOP concept. Polymorphism means the ability to take more than one form. For example, an operation may exhibit different behavior in different instances. The behavior depends upon the types of data used in the operation. For example consider the operation of addition. For two numbers, the operation will generate a sum. If the operands are strings, then the operation would produce a third string by Concatenation. Figure illustrates that a single function name can be used to handle different number and different types of arguments. This is something similar to a particular word having several different meanings depending on the context.

Polymorphism plays an important role in allowing objects having different internal structures to share the same external interface. This means that a general class of operation may be accessed in the same manner even though specific actions associated with each operation may differ. Polymorphism is extensively used in implementing inheritance.

Inheritance:

Inheritance is the process by which objects of one class acquire the properties of objects of another class. Inheritance supports the concept of hierarchical classification. For example, the bird robin is a part of the class flying bird, which is again a part of the class bird. As illustrated in Fig. 1.4, the principle behind this sort of division is that each derived class shares common characteristics with the class from which it is derived.

Property Inheritance 

 In 00P, the concept of inheritance provides the idea of reusability. This means that we can add additional features to an existing class without modifying it. This is possible by deriving a new class from the existing one. The new class will have the combined features of both the classes. Thus the real appeal and power of the inheritance mechanism is that it allows the Programmer to reuse a class that is almost, but not exactly, what he wants, and to tailor the class in such a way that it does not in introduce any undesirable side effects into the rest of the classes.In Java, the derived class is known as 'subclass'. Note that each subclass defines only those features that are unique to it. without the use of inheritance. each class Would have to explicitly include all of its features.

Data Abstraction and Encapsulation

Data Abstraction:

The wrapping up of data and methods into a single unit (called class) is known as encapsulation. Data encapsulation is the most striking feature of a class. The data is not accessible to_the outside world and only those methods, which are wrapped in the class, can access it. These methods provide the interface between the object's data and the program. This insulation of the data from direct access by the program is called data hiding. Encapsulation makes it possible tor objects to be treated like 'black boxes', each performing a specific task without any concern for internal implementation

 

Abstraction refers to the act of representing essential features without including the background details or explanations. Classes use the concept of abstraction and are defined as a list of abstract attributes such as size, weight and cost, and methods that operate on these attributes. They encapsulate all the essential properties of the objects that are to be created.