object orientation

What is object orientation?

The term object orientation (OO) means that we organize software as a collection of discrete objects that incorporate both data structure and behavior.

There is some dispute about exactly what characteristics are required by an OO approach, but they generally include four aspects:

1.      identity,

2.      classification,

3.      inheritance,

4.      Polymorphism.

Identity means that data is quantized into discrete, distinguishable entities called objects. Workstation and the white queen in a chess game are examples of objects.

Classification means that objects with the same data structure (attributes) and behavior (operations) are grouped into a class. Paragraph, Monitor, and Chess Piece are examples of classes.

A Class is an abstraction that describes properties important to an application and ignores the rest. Any choice of classes is arbitrary and depends on the application.  

Each class describes a possibly infinite set of individual objects. Each object is said to be an instance of its class. An object has its own value of each attribute but shares the attribute names and operations with other instances of the class.

Inheritance is a kind of attributes and operations (features) among classes based on a hierarchical relationship. A super class has general information that subclasses refine and elaborate. Each subclass incorporates, or inherits; all the features of its super class and adds its own unique features. Subclasses need not repeat the features of the super class. For example, scrolling Window and fixed window are subclasses of window. Both subclasses inherit the features of window, such as visible region on the screen. Scrolling Window adds a scroll bar and an offset. The ability to factor out common features of several classes into a super class can greatly reduce repetition within design and programs and is one of the main advantages of OO technology.

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Inheritance allows the extension and reuse of existing code, without having to repeat or rewrite the code from scratch. Inheritance involves the creation of new classes, also called derived classes, from existing classes (base classes). Allowing the creation of new classes enables the existence of a hierarchy of classes that simulates the class and subclass concept of the real world. The new derived class inherits the members of the base class and also adds its own. For example, a banking system would expect to have customers, of which we keep information such as name, address, etc. A subclass of customer could be customers who are students, where not only we keep their name and address, but we also track the educational institution they are enrolled in.

Inheritance is mostly useful for two programming strategies: extension and specialization. Extension uses inheritance to develop new classes from existing ones by adding new features. Specialization makes use of inheritance to refine the behavior of a general class.

Polymorphism means that the same operation may behave differently for different classes. The move operation, for example, behaves differently for a pawn than for the in a chess game. An operation is a procedure or transformation that an object performs or is subject to. Right Justify, display, and move are examples of operations. An implementation of an operation by a specific class is called a method. Because an OO operator is polymorphic, it may have more than one method implementing it, each for a different class of object.

(or)

Polymorphism allows an object to be processed differently by data types and/or data classes. More precisely, it is the ability for different objects to respond to the same message in different ways. It allows a single name or operator to be associated with different operations, depending on the type of data it has passed, and gives the ability to redefine a method within a derived class. For example, given the student and business subclasses of customer in a banking system, a programmer would be able to defi ne different getInterestRate() methods in student and business to override the default interest getInterestRate() that is held in the customer class. While Java supports method overloading, it does not support operator overloading.  

Encapsulation

The process, or mechanism, by which you combine code and the data it manipulates into a single unit, is commonly referred to as encapsulation. Encapsulation provides a layer of security around manipulated data, protecting it from external interference and misuse. In Java, this is supported by classes and objects.

Data Abstraction

Real-world objects are very complex and it is very difficult to capture the complete details. Hence, OOP uses the concepts of abstraction and encapsulation. Abstraction is a design technique that focuses on the essential attributes and behavior. It is a named collection of essential attributes and behavior relevant to programming a given entity for a specific problem domain, relative to the perspective of the user.