Why Class Is Called User-Defined Data Type?


Heather Bennett

Class is a fundamental concept in object-oriented programming (OOP). It allows us to create our own data types, which are known as user-defined data types.

But why exactly is class called a user-defined data type? Let’s explore the reasons behind this terminology.

The Need for User-Defined Data Types

In programming, we often encounter situations where the built-in data types provided by the language are not sufficient to represent real-world entities or solve complex problems. For example, imagine we need to model a car in a software application. The built-in data types like integers and strings alone may not be enough to capture all the characteristics and behaviors of a car.

This is where user-defined data types come into play. They allow programmers to define their own data structures that can store multiple pieces of information and perform specific operations on that data.

Defining a Class

In most object-oriented programming languages, including Java, C++, and Python, a class is used to define a user-defined data type. A class serves as a blueprint or template for creating objects of that type.

To define a class, we use the class keyword followed by the name of the class. For example, let’s say we want to create a class called “Car”. We would write:

<b>class Car</b>:
    # Class definition goes here

Properties and Methods

A class consists of two main components: properties and methods.

Properties, also known as attributes or member variables, represent the characteristics or state of an object. For example, in our “Car” class, properties could include things like “color”, “brand”, and “year”.

Methods, also known as member functions, define the behavior or actions that an object can perform. For example, our “Car” class could have methods like “start_engine()”, “accelerate()”, and “brake()”.

Creating Objects from a Class

Once we have defined a class, we can create objects of that class. An object is an instance of a class and represents a specific entity or occurrence.

To create an object, we use the new keyword followed by the name of the class and any required arguments for its constructor (a special method used to initialize objects). For example:

<b>car1 = Car()</b>
car2 = Car()

Using Objects of User-Defined Data Types

Objects of user-defined data types allow us to work with complex data structures and perform operations on them. We can access their properties using the dot notation and invoke their methods using dot notation along with parentheses.

For example, suppose we want to change the color of our car object:

<b>car1.color = 'blue'</b>
print(car1.color)  # Output: blue

car1.accelerate()  # Invoking a method

The Power of User-Defined Data Types

User-defined data types, created using classes, are incredibly powerful because they allow us to encapsulate both data and behavior into a single entity. This makes our code more organized, modular, and reusable.

We can create multiple objects from a single class, each with its own unique set of properties and behavior. This flexibility enables us to model complex real-world systems and solve intricate problems efficiently.


In summary, a class is called a user-defined data type because it allows programmers to define their own data structures with properties and methods. By creating objects from these user-defined data types, we can work with complex data structures and perform operations on them. This ability to encapsulate data and behavior into a single entity makes classes a powerful tool in object-oriented programming.

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