This content originally appeared on HackerNoon and was authored by Maximiliano Contieri
Make your class hierarchy clear and flexible
TL;DR: Extract a common abstract class to mimic real-world structure.
Problems Addressed
- Duplicate Code
- Inappropriate Inheritance
- Shotgun Surgery
- Big Class
- Feature Envy
- High Coupling
- Concrete classes subclassified
- Parent class not abstract
Related Code Smells
https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xiv?embedable=true
https://hackernoon.com/code-smell-255-addressing-parallel-hierarchies-in-code?embedable=true
https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xiii?embedable=true
https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-ix-7rr33ol?embedable=true
https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxxiii?embedable=true
Steps
Identify common behaviors in both classes.
\
Create an abstract class with shared behavior and no implementation.
\
Move common logic to the abstract class.
\
Update subclasses to inherit from the abstract class.
Sample Code
Before
class Car {
void drive() {
System.out.println("Driving a car");
}
}
class Truck extends Car {
void load() {
System.out.println("Loading cargo");
}
void unload() {
System.out.println("Unloading cargo");
}
}
// Truck reuses driving method
// Overriding it would be another code smell
// Violating Liskov Substitution rule
After
abstract class Vehicle {
// 2. Create an abstract class
// with shared behavior and no implementation
abstract void drive();
// 1. Identify common behaviors in both classes
// 3. Move common logic to the abstract class
}
class Car extends Vehicle {
// 4. Update subclasses to inherit from the abstract class
void drive() {
System.out.println("Driving a car");
}
}
class Truck extends Vehicle {
// 4. Update subclasses to inherit from the abstract class
void drive() {
System.out.println("Driving a truck");
// Implementation is different than the car's
}
void load() {
System.out.println("Loading cargo");
}
void unload() {
System.out.println("Unloading cargo");
}
}
Type
- [x] Semi-Automatic
Safety
This refactoring is safe if you identify all common behaviors correctly and move one method at a time running the tests.
Why is the Code Better?
It reduces duplication, simplifies maintenance, and makes it easier to extend functionality by adding new concrete realizations.
How Does it Improve the Bijection?
By introducing an abstract class, the code better reflects the real-world hierarchy, creating a clear relationship between the generic and specific types.
Refactor with AI
| Without Proper Instructions | With Specific Instructions | |----|----| | ChatGPT | ChatGPT | | Claude | Claude | | Perplexity | Perplexity | | Copilot | Copilot | | Gemini | Gemini | | Meta AI | Meta AI |
Tags
- Inheritance
Related Refactorings
https://hackernoon.com/refactoring-013-eliminating-repeated-code-with-dry-principles?embedable=true
See also
https://refactoring.guru/es/extract-superclass?embedable=true
Credits
This article is part of the Refactoring Series.
https://maximilianocontieri.com/how-to-improve-your-code-with-easy-refactorings?embedable=true
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This content originally appeared on HackerNoon and was authored by Maximiliano Contieri
Maximiliano Contieri | Sciencx (2025-01-23T21:22:07+00:00) Refactoring 022 – Extract Common Ancestor. Retrieved from https://www.scien.cx/2025/01/23/refactoring-022-extract-common-ancestor/
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