Object-oriented programming. (0)

Object -oriented programming.
Object-oriented programming (OOP) is a programming paradigm that uses "objects" and their interactions to design applications and computer programs. Programming techniques may include features such as information hiding, data abstraction, encapsulation, modularity, polymorphism, and inheritance. It was not commonly used in mainstream software application development until the early 1990s. Many modern programming languages now support OOP.
Class
Defines the abstract characteristics of a thing (object), including the thing's characteristics (its attributes, fields or properties) and the thing's behaviors (the things it can do, or methods, operations or features). One might say that a class is a blueprint or factory that describes the nature of something. For example, the class Dog would consist of traits shared by all dogs , such as breed and fur color (characteristics), and the ability to bark and sit (behaviors). Classes provide modularity and structure in an object-oriented computer program . A class should typically be recognizable to a non-programmer familiar with the problem domain, meaning that the characteristics of the class should make sense in context . Also, the code for a class should be relatively self-contained (generally using encapsulation). Collectively, the properties and methods defined by a class are called members .
Object
A pattern (exemplar) of a class. The class of Dog defines all possible dogs by listing the characteristics and behaviors they can have; the object Lassie is one particular dog, with particular versions of the characteristics. A Dog has fur; Lassie has brown -and-white fur.
Method
An object's abilities. In language , methods (sometimes referred to as "functions") are verbs . Lassie, being a Dog, has the ability to bark. So bark() is one of Lassie's methods. She may have other methods as well, for example sit() or eat() or walk () or save_timmy(). Within the program, using a method usually affects only one particular object; all Dogs can bark, but you need only one particular dog to do the barking.
Inheritance
"Subclasses" are more specialized versions of a class, which inherit attributes and behaviors from their parent classes, and can introduce their own. For example, the class Dog might have sub-classes called Collie, Chihuahua , and GoldenRetriever. In this case , Lassie would be an instance of the Collie subclass. Suppose the Dog class defines a method called bark() and a property called furColor. Each of its sub-classes (Collie, Chihuahua, and GoldenRetriever) will inherit these members, meaning that the programmer only needs to write the code for them once . Each subclass can alter its inherited traits. For example, the Collie class might specify that the default furColor for a collie is brown-and-white. The Chihuahua subclass might specify that the bark() method produces a high pitch by default. Subclasses can also add new members. The Chihuahua subclass could add a method called tremble(). So an individual chihuahua instance would use a high-pitched bark() from the Chihuahua subclass, which in turn inherited the usual bark() from Dog. The chihuahua object would also have the tremble() method, but Lassie would not, because she is a Collie, not a Chihuahua. In fact , inheritance is an "a... is a" relationship between classes, while instantiation is an "is a" relationship between an object and a class: a Collie is a Dog ("a... is a"), but Lassie is a Collie ("is a"). Thus, the object named Lassie has the methods from both classes Collie and Dog. Multiple inheritance is inheritance from more than one ancestor class, neither of these ancestors being an ancestor of the other . For example, independent classes could define Dogs and Cats , and a Chimera object could be created from these two which inherits all the (multiple) behavior of cats and dogs. This is not always supported, as it can be hard both to implement and to use well.

Example

DEFINITION MODULE Counter ;

PROCEDURE InitialiseCounter(InitialValue: INTEGER );

PROCEDURE IncrementCounter;

PROCEDURE GetCounterValue(): INTEGER;

END Counter.

IMPLEMENTATION MODULE Counter;

VAR MyCounter: INTEGER;

PROCEDURE InitialiseCounter(InitialValue: INTEGER);

BEGIN

MyCounter := InitialValue;

END InitialiseCounter;

PROCEDURE IncrementCounter;

BEGIN

INC(MyCounter);

END IncrementCounter;

PROCEDURE GetCounterValue(): INTEGER;

BEGIN

RETURN MyCounter;

END GetCounterValue;

BEGIN

MyCounter := 0;

END Counter.

Summary

OOP can be used to translate from real -world phenomena to program elements (and vice versa). OOP was even invented for the purpose of physical modeling in the Simula -67 programming language. However, not everyone agrees that direct real-world mapping is facilitated by OOP, or is even a worthy goal ; Bertrand Meyer argues in Object-Oriented Software Construction that a program is not a model of the world but a model of some part of the world; "Reality is a cousin twice removed". At the same time, some principal limitations of OOP had been noted.