Understanding Inheritance in Object-Oriented Programming

Learning Java, C++, or Python?

If you are learning any of these languages, you must have come across the term OOP, i.e. Object-Oriented Programming. These are a few of the many languages that support the fundamental concept of OOP, which revolves around Objects and Classes.

Objects: In simple terms, an object is a real-world entity or a thing that can be distinctly identified. It can represent anything from a physical item, like a car or a book, to more abstract concepts like a person’s bank account or a specific date and time.

Classes: A class is like a blueprint or a set of instructions that defines how an object should be created. Think of a class as a template that helps create objects with similar features. For example, if a car is an object, the class would define what properties a typical car should have (like color, model, and speed) and what actions it can perform (like starting, stopping, and honking).

OOP is like viewing the world as a collection of interacting objects, and programming becomes a way of modeling and simulating these interactions in a computer program. It helps to organize and structure code.

The concepts of Object-Oriented Programming include Encapsulation, Inheritance, Polymorphism, Abstraction, etc.

This article aims to comprehend the concept of Inheritance — what it means, the different types, and why it’s important.

What is Inheritance ?

Inheritance allows a new class (subclass/derived class) to inherit attributes/characteristics and behaviors from an existing class (superclass/base class/parent class).

Suppose you want to create a program to represent different types of vehicles. In this, you might want to represent cars, motorcycles, etc. While creating Cars, you might create attributes like name, model, and methods like start_engine(), stop_engine(), etc. When you create the Motorcycle class, you will again define these attributes and methods. Now, this is where inheritance comes into play. Both cars and motorcycles fall into the category of Vehicles. Therefore, we can create a superclass Vehicles and define all the general attributes and methods in it. Then, Cars and Motorcycles, as subclasses, can simply inherit these attributes and methods from the superclass Vehicles.

Types of Inheritance

There is more than one way in which subclass can inherit the properties of superclass. This results in different types of inheritance, each differing in the manner in which the properties are inherited.

• Single Inheritance
  In this, the class inherits from only one superclass.
  Example, Car inheriting from Vehicle class.

• Multiple Inheritance.
  When the class inherits from more than one class.
  For example, Bat is both bird and mammal. It can be derived from both the classes.

• Multilevel inheritance.
  A class inherits from another class, and then a third class inherits from the second class, forming a chain.
  Example, The superclass is Person, the subclass is student. Now we can derive another subclass CollegeStudent from student.

• Hierarchical Inheritance:
  In hierarchical inheritance, multiple classes inherit from a single superclass. It’s like a tree structure.
  Like Circle, Square, Triangle all these classes can inherit from single Shape superclass.

• Hybrid (Virtual) Inheritance:
  Hybrid inheritance is a combination of multiple types of inheritance within a single program. It allows a class to inherit from more than one class, supporting both single and multiple, multilevel or hierarchical inheritances simultaneously.

• Multipath (Diamond) Inheritance:
  Multipath or Diamond Inheritance occurs when a class inherits from two classes that have a common ancestor.
  Example, Shape represents common properties of shapes, and subclasses Circle and Rectangle specialize in specific shapes. A class Drawing then inherits from both Circle and Rectangle, forming a diamond inheritance structure.

Why Inheritance?

1. Reusability: In the above examples, inheritance saved us from defining same attributes and methods again and again for subclasses, therefore one use of inheritance is code reusability.
2. Modularity: Modularity refers to the concept of breaking down a complex system into smaller, self-contained, and independent units, often called modules. Inheritance enhances modularity by organizing code into logical units. Each class represents a distinct module with its own set of attributes and methods.
3. Ease of Maintenance: Changes made to the base class automatically affect all its subclasses. This simplifies maintenance because modifications or updates can be made in one central location (the base class) rather than having to update each individual class.
4. Hierarchy and Organization: Inheritance introduces a hierarchy in the code, reflecting the relationships between different classes. This hierarchy mirrors real-world relationships, making the code more intuitive and easier to understand.
5. Encapsulation: Inheritance supports encapsulation, another OOP principle. Encapsulation involves bundling data (attributes) and the methods that operate on that data into a single unit (class). Inheritance allows for the extension of encapsulated features in a systematic and hierarchical manner.
6. Abstraction: Inheritance supports abstraction, allowing developers to create abstract base classes that define common characteristics without providing specific implementations. Subclasses then provide concrete implementations of these abstract concepts.

Points to Remember

1. The subclass can access the public and protected members (methods and attributes) of the base class. Private members of the base class are not directly accessible in the subclass.
2. Inheritance represents an “is-a” relationship. For example, if a Car class inherits from a Vehicle class, it implies that a car is a type of vehicle.
3. Inheritance is closely related to polymorphism. Objects of the derived class can be treated as objects of the base class, allowing for flexibility and code reuse.
4. Some classes may be designed to prevent inheritance. This is often done by marking the class or its members as final or sealed in certain programming languages.
5. The subclass can provide a specific implementation for a method that is already defined in the base class. This is known as method overriding. Method overriding allows customization of behavior in the subclass while maintaining the same method signature.

Note: Specifics of inheritance can vary between programming languages, so it’s essential to refer to the documentation of the language you are using for accurate and language-specific details.

Conclusion

In conclusion, inheritance is a foundational concept in Object-Oriented Programming, crucial for languages like Java, C++, or Python. It enables code reusability, modularity, and ease of maintenance by allowing subclasses to inherit attributes and behaviors from a superclass. The hierarchy it establishes mirrors real-world relationships, promoting code organization and intuitiveness. Inheritance supports encapsulation and abstraction, fostering the creation of abstract base classes and concrete implementations. Understanding the various types of inheritance and its key principles enhances developers’ ability to create well-structured and efficient object-oriented code.