In object-oriented programming (OOP), objects are the basic elements of a program. In fact, everything in OOP is an object: the variables, the functions, and even the classes themselves. As you might imagine, working with objects can be quite complex. But with a little practice, you’ll find that object-oriented programming is one of the most powerful tools in your programming arsenal. In this article, we’ll take a look at some simple object-oriented programming examples in action to help you understand what OOP is all about.
What Is Object-Oriented Programming in Simple Terms?
OOP Explained
OOP is a style of programming that focuses on using objects to model real-world entities. One of object-oriented programming examples could be a representation of a planet in a solar system. This object would have properties like mass, radius, and orbital period. It would also have methods, or actions that it can perform, like rotating or orbiting another object.
In object-oriented programming, you would create a blueprint for this object, and then you could create as many planets as you wanted by using that blueprint. This is in contrast to procedural programming, where you would write a list of instructions to perform a task. With OOP, you instead create objects that know how to do certain things and can interact with other objects.
Advantage #1: Make Code More Modular
One advantage of object-oriented programming is that it makes code more modular. This means that you can reuse objects in different programs, or even in different parts of the same program. For example, if you have an object that represents a planet, you could use that object in a program that simulates the solar system, or in a program that is just a database of planets.
Advantage #2: Make Code Easier To Understand
Another advantage of object-oriented programming is that it can make code easier to understand. This is because the objects represent real-world entities, so it can be easier to visualize what the code is doing. For example, if you have a program that simulates the solar system, it would be easier to understand if the code was organized into objects like planets, stars, and galaxies.
Disadvantage #1: Complex To Initially Understand
Of course, object-oriented programming is not the only way to write code, and it has its own disadvantages. One disadvantage is that object-oriented programming can be more complex than other styles of programming. This is because you have to design the objects and their interactions, which can be a lot of work.
Disadvantage #2: Can Be Slower To Execute
Another disadvantage is that object-oriented programming can make code slower, because the objects have to interact with each other, which takes processing time.
Despite these disadvantages, object-oriented programming is a powerful tool that can be used to write efficient and understandable code.
How Does Object-Oriented Programming Work?
In object-oriented programming, you create objects that represent real-world entities. These objects have properties and methods that describe the object. For example, a car object might have properties like color and make. It would also have methods like start and stop.
You can think of an object as a blueprint for creating a real-world entity. Once you have created an object, you can create multiple instances of that object. Each object instance would have its own unique properties and methods, but they would all be based on the original object blueprint.
One of the benefits of object-oriented programming is that you can create relationships between objects. For example, a car object can be related to a driver object. The car object would have a property that represents the driver object. This is called an object reference.
With object references, you can create complex interactions between objects. For example, you could make it so that the car object cannot be started unless the driver object is in the car. Or you could make it so that the driver object can only drive the car object if the car object has enough gas.
What Object-Oriented Programming Languages Are There?
There are many object-oriented programming languages, but some of the most popular ones are Java, C++, and Python.
Java
Java is a widely used object-oriented programming language that runs on all major operating systems. It is used in many large software projects, such as Android, Eclipse, and Hadoop. Java is the language we will use for our object-oriented programming examples below.
C++
C++ is another popular object-oriented programming language. It is used in many large projects, such as Microsoft Windows, Adobe Photoshop, and Mozilla Firefox.
Python
Python is a newer object-oriented programming language that has gained popularity in recent years. It is used in many small projects, such as Raspberry Pi and Django.
Difference Between OOP Languages
What is the difference between these languages if they are all OOP languages? The main difference is in the way they handle object references. In Java and C++, object references are stored in memory, which can make code slower. In Python, object references are not stored in memory, which can make code faster.
There are many other differences as well such as syntax and type systems. All of which are decisions made to improve the languages in specific domains.
What Are the Simple Concepts in OOP? (Classes, Properties, Methods)
In order to understand the object-oriented programming examples we outline in this article, we will first need to take a closer look at some of the simple concepts in object-oriented programming.
Classes
A class is a blueprint for creating objects. It is a template for an object, and it defines the object’s properties and methods. For example, you could create a class for a car object. The class would define the car object’s properties, such as color and make. It would also define the car object’s methods, such as start and stop.
Properties
A property is a characteristic of an object. It is a value that describes the object. For example, a car object might have properties like color and make.
Methods
A method is an action that can be performed on an object. It is a function that is associated with an object. For example, a car object might have methods like start and stop.
Objects
An object is an instance of a class. It is a concrete representation of the class. For example, if you have a class for a car object, then an object would be a specific car, such as a Ford Mustang or a Toyota Camry.
Object references
An object reference is a link between two objects. It is a value that represents an object. For example, a car object might have a property that represents the driver object. This would be an object reference.
With object references, you can create complex interactions between objects. For example, you could make it so that the car object cannot be started unless the driver object is in the car. Or you could make it so that the driver object can only drive the car object if the car object has enough gas.
In the next section, we will look at some object-oriented programming examples and concepts.
What Are Some Simple Object-Oriented Programming Examples?
Let’s review several simple object-oriented programming examples to better understand how the model works and how it is structured.
1. Countries, Capitals, and Cities
In this example, we have three object types: countries, capitals, and cities. Each object type has its own properties and methods.
The country object has properties like name and population. It also has methods like getCapital and getCities, which return the capital object and city objects, respectively.
The capital object has properties like name and population. It also has a method called getCountry, which returns the country object that this capital belongs to.
The city object has properties like name and population. It also has a method called getCountry, which, again, returns the country that this city is a part of.
Let’s put these three classes in Java code:
public class Country {
// properties
private String name;
private int population;
// methods
public Country(String name, int population) {
this.name = name;
this.population = population;
}
public String getName() {
return this.name;
}
public int getPopulation() {
return this.population;
}
public Capital getCapital() {
// returns the capital object
}
public ArrayList<City> getCities() {
// returns a list of city objects
}
}
public class Capital {
// properties
private String name;
private int population;
// methods
public Capital(String name, int population) {
this.name = name;
this.population = population;
}
public String getName() {
return this.name;
}
public int getPopulation() {
return this.population;
}
public Country getCountry() {
// returns the country object that this capital belongs to
}
}
public class City {
// properties
private String name;
private int population;
// methods
public City(String name, int population) {
this.name = name;
this.population = population;
}
public String getName() {
return this.name;
}
public int getPopulation() {
return this.population;
}
public Country getCountry() {
// returns the country object that this city is a part of
}
}
As you can see from this example, Country, Capital, and City are classes that interact with each other, thus creating object references. The Country class has a property called name and a method called getCapital, which returns the Capital object. The Capital class has a property called name and a method called getCountry, which returns the Country object. And finally, the City class has a property called name and a method called getCountry, which again returns the Country object.
It is evident how this structure of the program can easily become more complex with the addition of more object types and relationships. However, object-oriented programming provides a way to manage this complexity by breaking down a program into smaller, more manageable pieces.
2. Students, Teachers, and Classes
In this example, we have three object types: students, teachers, and classes. Each object type has its own properties and methods.
The student object has properties like name and age. It also has a method called getClasses, which returns the class objects that this student is taking.
The teacher object has properties like name and age. It also has a method called getClasses, which returns the class objects that this teacher is teaching.
The class object has properties like name and room number. It also has methods called getStudents and getTeacher, which return the student objects and teacher object, respectively, that are associated with this class.
Let’s put these three classes in Java code:
public class Student {
// properties
private String name;
private int age;
// methods
public Student(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return this.name;
}
public int getAge() {
return this.age;
}
public ArrayList<Class> getClasses() {
// returns a list of Class objects that this student is taking
}
}
public class Teacher {
// properties
private String name;
private int age;
// methods
public Teacher(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return this.name;
}
public int getAge() {
return this.age;
}
public ArrayList<Class> getClasses() {
// returns a list of Class objects that this teacher is teaching
}
}
public class Class {
// properties
private String name; // e.g. "Math"
private int roomNumber; // e.g. "102"
// methods
public Class(String name, int roomNumber) {
this.name = name;
this.roomNumber = roomNumber;
}
public String getName() {
return this.name;
}
public int getRoomNumber() {
return this.roomNumber;
}
public ArrayList<Student> getStudents() {
// returns a list of Student objects that are taking this class
}
public Teacher getTeacher() {
// returns the Teacher object that is teaching this class
}
}
In this example, we can see how object-oriented programming can be used to model real-world relationships. The student object is associated with the class object, and the teacher object is associated with the class object. These relationships are represented by the methods in each object.
3. Online Shopping
Another object-oriented programming example is an online shopping system. In this system, we have four object types: user, product, order, and payment. Each object type has its own properties and methods.
The user object has properties like name and address. It also has methods like getOrders and getPayments, which return the order and payment objects, respectively, that are associated with this user.
The product object has properties like name and price. It also has a method called getOrders, which returns the order objects that are associated with this product.
The order object has properties like quantity and date. It also has methods called getUser and getProduct, which return the user object and product object, respectively, that are associated with this order.
The payment object has properties like amount and date. It also has a method called getUser, which returns the user object that is associated with this payment.
Let’s put these four classes in Java code:
public class User {
// properties
private String name;
private String address;
// methods
public User(String name, String address) {
this.name = name;
this.address = address;
}
public String getName() {
return this.name;
}
public String getAddress() {
return this.address;
}
public ArrayList<Order> getOrders() {
// returns a list of Order objects that this user has made
}
public ArrayList<Payment> getPayments() {
// returns a list of Payment objects that this user has made
}
}
public class Product {
// properties
private String name; // e.g. "iPhone"
private double price; // e.g. 699.99
// methods
public Product(String name, double price) {
this.name = name;
this.price = price;
}
public String getName() {
return this.name;
}
public double getPrice() {
return this.price;
}
public ArrayList<Order> getOrders() {
// returns a list of Order objects that are associated with this product
}
}
public class Order {
// properties
private int quantity; // e.g. 1
private Date date; // e.g. "02-20-2023"
// methods
public Order(int quantity, Date date) {
this.quantity = quantity;
this.date = date;
}
public int getQuantity() {
return this.quantity;
}
public Date getDate() {
return this.date;
}
public User getUser() {
// returns the User object that made this order
}
public Product getProduct() {
// returns the Product object that this order is for
}
}
public class Payment {
// properties
private double amount; // e.g. 89.99
private Date date; // e.g. "02-20-2023"
// methods
public Payment(double amount, Date date) {
this.amount = amount;
this.date = date;
}
public double getAmount() {
return this.amount;
}
public Date getDate() {
return this.date;
}
public User getUser() {
// returns the User object that made this payment
}
}
In this example, each object is associated with one or more other objects. For example, the User object is associated with the Order and Payment objects. This relationship is called an association.
Associations can be one-to-one, one-to-many, or many-to-many. In the example above, the association between User and Order is one-to-many, because one user can make many orders. The association between User and Payment is also one-to-many, because one user can make many payments. The association between Product and Order is many-to-many, because one product can be ordered by many users, and one user can order many products.
In object-oriented programming, associations are typically represented by references. For example, the User object has a reference to the Order object. In Java code, this would be represented like this:
public class User {
// ... properties and methods omitted for brevity ...
// reference to the Order object
private Order order;
public void setOrder(Order order) {
this.order = order;
}
public Order getOrder() {
return this.order;
}
}
In this code, the User object has a property called order, which is a reference to an Order object. The setOrder() method is used to set the value of this property, and the getOrder() method is used to get the value of this property.Similarly, the Order object has a reference to the User object:
public class Order {
// ... properties and methods omitted for brevity ...
// reference to the User object
private User user;
public void setUser(User user) {
this.user = user;
}
public User getUser() {
return this.user;
}
}
In this code, the Order object has a property called user, which is a reference to a User object. The setUser() method is used to set the value of this property, and the getUser() method is used to get the value of this property.
You can use associations to represent relationships between objects in your code. For example, you could use an association to represent the relationship between a customer and their orders.
What Are More Advanced Concepts in OOP?
Besides the simple OOP concepts we outlined in our object-oriented programming examples above, there are many more advanced concepts in object-oriented programming, such as inheritance, polymorphism, abstraction, and interfaces. Let’s break down these concepts one-by-one in a simple and understandable way.
Inheritance
In object-oriented programming, inheritance is when one object is a specialized version of another object. For example, you could have a User object and a Customer object, where the Customer object inherits from the User object. In this case, the Customer object would have all the same properties and methods as the User object, plus some additional properties and methods that are specific to customers.
In Java, inheritance is represented by the extends keyword. For example:
public class Customer extends User {
// ... properties and methods specific to customers ...
}
In this code, the Customer object inherits from the User object. This means that the Customer object has all the same properties and methods as the User object, plus some additional properties and methods that are specific to customers.
Polymorphism
In object-oriented programming, polymorphism is when you have multiple objects that share the same interface. For example, you could have a Shape object and a Square object, where the Square object inherits from the Shape object. In this case, both the Shape object and the Square object would have a method called draw(), but the implementation of this method would be different for each object.
In Java, polymorphism is represented by the keyword override. For example:
public class Shape {
// ... properties and methods common to all shapes ...
public void draw() {
// ... code to draw the shape ...
}
}
public class Square extends Shape {
// ... properties and methods specific to squares ...
@Override
public void draw() {
// ... code to draw the square ...
}
}
In this code, the Square object inherits from the Shape object. Both objects have a method called draw(), but the implementation of this method is different for each object. The Square object overrides the draw() method from the Shape object, which means that the Square object’s draw() method will be called instead of the Shape object’s draw() method.
Abstraction
In object-oriented programming, abstraction is when you have an object that represents something abstract, which has a set of properties, but is not actually identified. For example, you could have an Object called CelestialBody that represents a star, planet, or moon. This object would have properties like name and mass, and methods like getGravity().
In Java, abstraction is represented by the keyword abstract. For example:
public abstract class CelestialBody {
// ... properties like name and mass ...
public abstract double getGravity();
// ... other methods ...
}
In this code, the CelestialBody object is declared as abstract, which means that it cannot be instantiated. It is an abstract item with a set of properties and methods, but it is not by itself an identifiable thing. This object has a method called getGravity(), which is also declared as abstract. This means that the getGravity() method must be implemented by a non-abstract class that inherits from CelestialBody.
Interfaces
In object-oriented programming, an interface is like a contract that specifies a set of methods that an object must implement. For example, you could have an Interface called Movable that specifies a set of methods like move() and stop(). Any object that implements the Movable interface must have these methods.
In Java, an interface is represented by the keyword interface. For example:
public interface Movable {
void move();
void stop();
}
In this code, the Movable interface is declared. This interface has two methods, move() and stop(). Any object that implements the Movable interface must have these methods.
How to Learn Object-Oriented Programming?
Object-oriented programming is one of the most in-demand hard skills for software developers and is often asked in coding interviews.
Learning object-oriented programming can be tricky, but there are a lot of resources available to help you. Here are some recommendations:
University courses
Object-oriented programming is often a part of the computer science curriculum within regular CS degree programs. If you are a university student, it is likely you will study the OOP principles and languages extensively throughout your college education.
Online courses
- Python Beyond the Basics on Udemy – This is a great online course that covers everything you need to know about object-oriented programming.
- Object-Oriented Programming in Java on Coursera – This is a comprehensive online course that covers object-oriented programming in Java.
- Object-Oriented Data Structures in C++ on Coursera – This great online course covers OOP in C++.
If you are unsure which learning platform works better for you, check out this comparison article of Udemy vs. Coursera platforms on IQ Unlock.
Books
- Head First Object-Oriented Analysis and Design by Brett D. McLaughlin, Gary Pollice, Dave West – This classic book covers everything you need to know about object-oriented design and analysis.
- Clean Code by Robert C. Martin – This book is essential reading for any programmer. It covers best practices for object-oriented programming, and will help you write cleaner and more maintainable code.
- Elegant Objects by Yegor Bugayenko – This book covers object-oriented design principles and patterns in great detail.
Conclusion
Object-oriented programming (OOP) is a programming paradigm that uses objects to model the real world. In OOP, you create classes and objects, and then use those objects to build programs. OOP is a popular way of programming because it allows you to easily create complex systems by breaking them down into smaller, more manageable pieces. There are many different object-oriented languages, but the most popular ones are Java, C++, and Python. In this article, we have covered the basics of OOP, including object-oriented programming examples, what OOP is, its benefits, and how to learn it.
As always, happy coding!
