Object-Oriented Programming
Internal
Overview
Object-oriented programming is first and foremost about message passing between class instances.
Object-Oriented Analysis and Design
In software development, design is often assumed to happen before programming. In reality, analysis, programming and design ten to overlay, combine and interweave. Object-oriented analysis is the process of looking at a problem, system or task, with the intention of creating an application that addresses it, and identifying the objects and interactions between objects. The analysis stage is about what needs to be done.
The output of the analysis stage is a set of requirements.
Object-oriented design (OOD) is the process of converting the requirements into an implementation specification. The designer names the objects, defines their behaviors and formally specifies which objects can activate specific behaviors on other objects. This stage is about how things should be done.
The output of the design stage is the implementation specification.
In most cases, all these stages overlap and the development happens in an iterative model, in which a small part of the project is modeled, designed and programmed, and then the program is iteratively reviewed and expanded.
Object-Oriented Programming vs Functional Programming
Class
A class represents a type of thing and concept. Classes defines state - what kind of information, or attributes they can store. Classes also define behavior, or methods.
Objects
An object is a specific instance of a class.
Inheritance
The inheritance implies that there are classes that are very generic, and other classes that are specific. The specific classes can inherit specific attributes and behavior from generic classes, and they can also have specific attributes and behaviors that are particular to them, and to no one else. Thus, classes form hierarchies.
Parent types are called superclasses. Subtypes are called subclasses.
The motivation behind inheritance is code reusability. If something that is generally applicable to a set of classes, that belongs into the superclass, which can be then inherited.