What Is a Class Data Type?


Larry Thompson

What Is a Class Data Type?

A class data type is an essential concept in object-oriented programming (OOP). It allows programmers to create their own custom data types by combining variables and functions into a single entity known as a class.

In this article, we will explore the concept of a class data type and understand how it is used in practice.

Defining a Class

To define a class in HTML, we use the <class> tag. Within this tag, we can define various properties and methods that characterize the class. Let’s look at an example:


In the example above, we define a class with one property called “name” of type string and one method called “sayHello” that takes no parameters and returns nothing (void).

Creating Objects from a Class

Once we have defined a class, we can create objects from it. An object is an instance of a class and represents a specific entity with its own unique characteristics.

To create an object in HTML, we use the <object> tag.

<object data="MyClass" id="myObject"></object>

In the example above, we create an object named “myObject” from the class “MyClass”. This object now has access to all the properties and methods defined in the class.

Accessing Class Members

To access the properties and methods of a class, we use dot notation. For example, to set the value of the “name” property of our object, we can use:

    document.getElementById("myObject").name = "John";

Similarly, to call a method on our object, we can use:


Inheritance and Polymorphism

One of the key features of classes is inheritance. Inheritance allows us to create new classes based on existing ones, inheriting their properties and methods.

This promotes code reusability and modularity.

Polymorphism is another important concept in OOP that allows objects of different classes to be treated as objects of a common superclass. This enables us to write more generic code that can work with different types of objects.


In summary, a class data type is a fundamental building block in OOP. It provides a way to define custom data types by combining variables and functions into a single entity. By creating objects from these classes, we can work with specific instances of these data types and leverage their properties and methods.

Inheritance and polymorphism further enhance the flexibility and reusability of our code. Understanding how to define and use class data types is crucial for any programmer aiming to harness the power of object-oriented programming.

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