Disadvantages of Inheritance in Java

Inheritance stands as a fundamental principle among the four main components of Object-Oriented Programming (OOP) in Java. Symbolically, inheritance allows subclasses to acquire all superclass fields and methods through this relationship.

The feature enables developers to reuse code blocks and create maintainable and expandable programs, leading to effective Java development. The inheritance model brings specific drawbacks that include complicated code structures as well as strengthened relations between different classes.

1. Increases Coupling Between Parent and Child Classes

The parent-child class relationship becomes closely linked because of inheritance. Changes implemented on the parent class could impact every single child class, creating the possibility of introducing unwanted bugs.

Example: All child classes needing to use a method from the parent class must receive updates after this method gets changed or damaged. The inheritance structure creates difficult-to-support codebases that are also brittle in nature.

2. Inherits Unnecessary Methods and Properties

Subclasses inherit all the public and protected members of the superclass, even if they are not needed. This can lead to memory wastage and unnecessary complexity in subclasses.

Here, the Bicycle class inherits the startEngine() method even though it does not make sense for a bicycle.

3. Reduces Flexibility and Forces a Rigid Hierarchy

Inheritance enforces a strict hierarchical relationship, which may not always be the best approach for some applications. Composition (using objects of other classes instead of inheritance) is often a better alternative when flexibility is required.

Here, Car has-a Engine instead of inheriting from Engine, making the relationship more flexible.

4. Increases Complexity and Makes Debugging Difficult

In a deeply inherited class structure, debugging can become challenging since an issue in a subclass might be caused by an inherited method from multiple levels above. This can lead to spaghetti code, making it harder to trace errors.

5. Performance Overhead

The inheritance mechanism requires extra steps to resolve methods, which generates small decreases in system performance. Modern Java Virtual Machines operate efficiently with inheritance, but performance vital applications need to control inheritance usage to prevent execution speed reduction.

6. Breaks Encapsulation

The public nature of inheritance accessibility allows subclasses to view superclass implementation details contrary to the encapsulation principle. The protected variables and methods in the superclass become accessible for modification through subclasses, which might lead to unexpected outcomes.

7. Tight Coupling Makes Refactoring Difficult

If a superclass is modified, all subclasses are affected, making refactoring difficult. A minor change in a base class can lead to unintended side effects in multiple derived classes, increasing maintenance complexity.

8. Difficulty in Unit Testing

Testing subclasses becomes harder when they depend on inherited methods from superclasses. Mocking and testing such dependencies require additional effort, making unit testing complex.