Object-Oriented Programming Concepts

Object-oriented programming (OOP) is a programming paradigm that uses "objects" – data structures consisting ofdata fields and methods together with their interactions – to design applications and computer programs. Programming techniques may include features such as 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.

There are several part to know what OOP is,

1. Object and Class

2. Instance

3. Method

4. Message passing

5. Inheritance

6. Abstraction

7. Encapsulation

8. (Subtype) polymorphism

9. Decoupling

Object and Class

A Class is a user defined datatype which contains the variables, properties and methods in it. A class defines the abstract characteristics of a thing (object), including its 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.

instance

One can have an instance of a class; the instance is the actual object created at run-time. In programmer vernacular,the Lassie object is an instance of the Dogclass. The set of values of the attributes of a particular object is called its state. The object consists of state and the behavior that's defined in the object's classes

Method

Method is a set of procedural statements for achieving the desired result. It performs different kinds of operations on different data types. In a programming 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

Message passing

"The process by which an object sends data to another object or asks the other object to invoke a method."^[13] Also known to some programming languages as interfacing. For example, the object called Breeder may tell the Lassie object to sit by passing a "sit" message which invokes Lassie's "sit" method. The syntax varies between languages, for example: [Lassie sit] in Objective-C. In Java, code-level message passing corresponds to "method calling". Some dynamic languages use double-dispatch or multi-dispatch to find and pass messages.

Inheritance

Inheritance is a process in which a class inherits all the state and behavior of another class. this type of relationship is called child-Parent or is-a relationship. "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 theCollie subclass. Suppose the Dog class defines a method called bark() and a property called furColor. Each of its sub-classes (Collie, Chihuahua, andGoldenRetriever) 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 subclass might specify that the default furColor for a collie is brown-and-white. TheChihuahua subclass might specify that the bark() method produces a high pitch by default. Subclasses can also add new members. The Chihuahuasubclass 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: aCollie 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 to implement.

Abstraction

Abstraction is simplifying complex reality by modeling classes appropriate to the problem, and working at the most appropriate level of inheritance for a given aspect of the problem.

For example, Lassie the Dog may be treated as a Dog much of the time, a Collie when necessary to access Collie-specific attributes or behaviors, and as an Animal (perhaps the parent class of Dog) when counting Timmy's pets.

Encapsulation

Encapsulation conceals the functional details of a class from objects that send messages to it.

For example, the Dog class has a bark() method variable,data. The code for the bark() method defines exactly how a bark happens (e.g., by inhale() and then exhale(), at a particular pitch and volume). Timmy, Lassie's friend, however, does not need to know exactly how she barks. Encapsulation is achieved by specifying which classes may use the members of an object. The result is that each object exposes to any class a certain interface — those members accessible to that class. The reason for encapsulation is to prevent clients of an interface from depending on those parts of the implementation that are likely to change in the future, thereby allowing those changes to be made more easily, that is, without changes to clients. For example, an interface can ensure that puppies can only be added to an object of the class Dog by code in that class. Members are often specified as public, protected or private, determining whether they are available to all classes, sub-classes or only the defining class. Some languages go further: Java uses the default access modifier to restrict access also to classes in the same package, C# and VB.NET reserve some members to classes in the same assembly using keywords internal (C#) or Friend (VB.NET). Eiffel and C++ allow one to specify which classes may access any member.

Polymorphism

Polymorphism allows the programmer to treat derived class members just like their parent class's members. More precisely, Polymorphism in object-oriented programming is the ability of objects belonging to different data types to respond to calls of methods of the same name, each one according to an appropriate type-specific behavior. One method, or an operator such as +, -, or *, can be abstractly applied in many different situations. If a Dog is commanded to speak(), this may elicit a bark(). However, if a Pig is commanded to speak(), this may elicit an oink(). Each subclass overrides the speak() method inherited from the parent class Animal.

Decoupling

Decoupling allows for the separation of object interactions from classes and inheritance into distinct layers of abstraction. A common use of decoupling is to polymorphically decouple the encapsulation, which is the practice of using reusable code to prevent discrete code modules from interacting with each other. However, in practice decoupling often involves trade-offs with regard to which patterns of change to favor. The science of measuring these trade-offs in respect to actual change in an objective way is still in its infancy.