What Is Object-Oriented Programming (OOP)? A Complete Guide

Updated February 3, 2023

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As technology advances, many companies continue to have a high demand for employees with knowledge of computer programming. A common classification among many programming languages is object-oriented programming (OOP). As a developer or programmer, understanding OOP can help you create and maintain software programs using various languages.

In this article, we discuss object-oriented programming, its structure and its core principles, and we describe the benefits of this programming style.

What is object-oriented programming?

Object-oriented programming is a programming paradigm, or classification, that organizes a group of data attributes with functions or methods into a unit, known as an object. Typically, OOP languages are class-based, meaning a class defines the data attributes and functions as a blueprint for creating objects, which are instances of the class. One class may represent multiple independent objects, which interact with each other in complex ways. Popular class-based programming languages include Java, Python and C++.

For example, if a class represents a person, it may contain attributes to represent various data, such as the person's age, name and height. The class definition might also contain functions, such as a function to print the person's name on a screen. You could create a family by representing person objects from the class of each family member. Each person object contains different data attributes because every person is unique.

Structure of object-oriented programming

Object-oriented programming contains various structures, known as the building blocks of OOP. These structures include:

Class: A class is a data type that provides a framework for creating objects. You can define a class to create multiple objects without writing additional code.

Object: In OOP, an object represents an instance, or creation, of a class. Objects define specific data, such as properties and behaviors, to implement code.

Method: A method is a function that performs a task or action. For example, a method may return information about an object's data.

Attribute: This structure stores information about an object and defines its state. You can define an attribute as part of the class.

4 principles of object-oriented programming

Object-oriented programming has four basic concepts: encapsulation, abstraction, inheritance and polymorphism. Knowing how they work together can help you understand the basic functionality of an OOP computer program. Review the explanation for each concept and explore examples to help you understand them:

1. Encapsulation

Encapsulation means to enclose data by containing it within an object. In OOP, encapsulation forms a barrier around data to protect it from the rest of the code. You can perform encapsulation by binding the data and its functions into a class. This action conceals the private details of a class and only exposes the functionality essential for interfacing with it. When a class doesn't allow direct access to its private data, it's well-encapsulated.

Example

When creating a class to represent a person, you may define private data, such as the person's Social Security Number. You can encapsulate this data as a private variable in the class, which means outside code can't access it. If you write a method in the person class to perform a bank transaction, the function could access the data variable as necessary. In this example, the person's private data is well-encapsulated within the class.

2. Abstraction

Abstraction refers to using simplified classes, rather than complex implementation code, to access objects. Often, it's easier to design a program when you can separate the interface of a class from its implementation. In OOP, you can abstract the implementation details of a class and present a clean, easy-to-use interface through the class member functions. Abstraction helps isolate the impact of changes made to the code so if an error occurs, the change only affects the implementation details of a class and not the outside code.

Example 1

Consider a stereo system as an object with a complex logic board on the inside. The stereo system has buttons on the outside to allow for interaction with the object. When you press a button, the logic board completes a function to turn on the system, even though you can't see what happens inside the board. This example represents the concept of abstraction, which you can apply widely in object-oriented programming.

Example 2

In OOP, you might define a class to represent the human body. You can define some functions as part of its public interface, such as walking or eating food. Using abstraction, it's not necessary to write code to explain the bodily functions allowing a person to walk or eat. Instead, you can create simple functions abstracted from the end user to represent this information.

3. Inheritance

Most object-oriented languages support inheritance, which means a new class automatically inhabits the same properties and functionalities as its parent class. Inheritance allows you to organize classes into hierarchies, where a class might have one or more parent or child classes. If a class has a parent class, it means the class has inherited the properties of the parent. The child class can also modify or extend the behavior of its parent class. Inheritance allows you to reuse code without redefining the functions of a child class.

Example

For instance, in the animal world, an insect may belong to an insect class. In this class, all insects share similar properties, such as having six legs and an exoskeleton. You can create subclasses for different varieties of insects, such as grasshoppers and ants. These child classes inherit the properties of the insect class, meaning they share those same features.

4. Polymorphism

Polymorphism refers to creating objects with shared behaviors. In OOP, polymorphism allows for the uniform treatment of classes in a hierarchy. When you write code for objects at the root of the hierarchy, any objects created by a child class within the hierarchy have the same functions. Depending on the type of object, it may execute different behaviors.

Example

If you have a class called animal with two child classes, cat and dog, you can create a class function to make a noise. Using polymorphism, you can override this function inherited by the cat and dog child classes. Instead, you can make this function "meow" and "bark" for cat and dog, respectively. Depending on the type of animal object that passes through the interface, it either makes a "meow" or a "bark" noise.

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Benefits of object-oriented programming

Object-oriented programming is a popular programming style in many languages. By defining sets of classes that represent and encapsulate objects in a program, OOP can organize classes into modules, improving the structure of software programs. It's common for software developers to use OOP when creating complex programs because it allows them to define classes and their relationships. Other benefits of OOP include:

Reusable code: The inheritance principle of OOP allows you to reuse code without writing it repeatedly. This feature can help to reduce errors when creating code.
Increased productivity: By creating objects from classes, you can save time when developing new software. You can also use libraries and reusable code to increase your productivity.
Enhanced security: You can use encapsulation and abstraction to display limited data while concealing sensitive information. These features can provide enhanced security when developing complex code.

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