Last updated on Jul 13, 2024

How do you design reusable classes with inheritance?

In object oriented design, inheritance is a powerful mechanism that allows you to reuse existing classes and extend their functionality. Inheritance enables you to create new classes that inherit the attributes and methods of their parent classes, while adding or overriding some of them. This way, you can avoid code duplication, enhance modularity, and promote code reuse. However, designing reusable classes with inheritance requires careful planning and attention to some principles and best practices. In this article, you will learn how to design reusable classes with inheritance in four steps.

1 Step 1: Identify the common features

The first step is to identify the common features that you want to reuse in different classes. These features can be data attributes, such as name, age, or color, or methods, such as get, set, or print. You can use various techniques, such as brainstorming, use cases, or class diagrams, to find out the common features. For example, if you want to design reusable classes for different types of animals, you might identify some common features, such as name, age, weight, sound, and eat.

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Amruta Jahagirdar

"Experienced .NET Architect | Masters in Computer Science | Author, Mentor, AI Enthusiast | Transforming Ideas into Innovative Solutions for 14 Years"
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Identify common behaviours, attributes, and methods shared among multiple classes. These commonalities form the basis for the parent class (baseclass) in the inheritance hierarchy. Create a base class that encapsulates the common functionality shared by subclasses. This class serves as a blueprint for creating subclasses and defines the common attributes and methods that will be inherited by them.

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Jagan Turlapati

Senior Software Engineer (.Net)
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Designing reusable classes with inheritance involves creating a class hierarchy that promotes code reuse, flexibility, and maintainability while adhering to principles of object-oriented design. Here are key strategies and best practices for designing reusable classes with inheritance:

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2 Step 2: Create the base class

The second step is to create the base class that will contain the common features that you identified in the previous step. The base class is also known as the superclass, parent class, or abstract class. You can use the class keyword to define the base class and its attributes and methods. For example, you can create a base class called Animal that has the attributes name, age, weight, and sound, and the methods get, set, and print.

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Gaurav Arora

SDE at HT Digital Streams | 3 X INSTA AWARD WINNER AT HT | Meta Hackercup AIR-51 2022 | Spring Boot | Microservices | System Design and DSA ❤️
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The base class is supposed to have all the attributes and methods that will be common in any child class of that class that is already created or could be created in the future. Thinking ahead of time and scope of a class before-hand is essential to choosing right attributes and methods of a class. We need to make sure not to add features to the base class which are going to be in few of the child classes and not in all.

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3 Step 3: Create the derived classes

The third step is to create the derived classes that will inherit the common features from the base class and add or modify some of them. The derived classes are also known as the subclasses, child classes, or concrete classes. You can use the extends keyword to specify the inheritance relationship between the derived class and the base class. For example, you can create a derived class called Dog that extends the Animal class and adds a new attribute called breed and a new method called bark.

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Amruta Jahagirdar

"Experienced .NET Architect | Masters in Computer Science | Author, Mentor, AI Enthusiast | Transforming Ideas into Innovative Solutions for 14 Years"
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Utilize inheritance to create subclasses that inherit from the parent class. Subclasses inherit all the attributes and methods of the parent class and can also define additional attributes and methods specific to their own functionality.

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4 Step 4: Apply the Liskov substitution principle

The fourth step is to apply the Liskov substitution principle, which is a design principle that states that a derived class should be able to substitute its base class without breaking the functionality of the program. This means that the derived class should not violate the contract or expectations of the base class, such as changing the meaning or behavior of its methods, or introducing new errors or exceptions. For example, if the Animal class has a method called eat that takes a parameter called food , the Dog class should not override this method and make it take a parameter called bone , because this would break the compatibility with the Animal class.