When you ignore your inheritance, you will have trouble with your parents TL;DR: Subclasses should honor ALL their parent’s contract. Problems 😔 Wrong abstraction
Subclassification for code reuse
Misleading hierarchy
Unused or overridden methods
Unnecessary complexity
Liskov Principle Violation
Maintenanabiilty
YoYo Hierachies
Concrete classes subclassified Solutions 😃 Favor composition over inheritance
Don't subclassify for code reuse
Rethink hierarchy
Extract shared logic
Use interfaces
Remove dead code Refactorings ⚙️ Refactoring 007 - Extract Class Context 💬 When you create a subclass, it should use or extend the behavior of its parent. If it ignores or overrides most of it, you probably force inheritance where it doesn’t belong to reuse code. This makes the code misleading and hard to maintain. Sample Code 📖 Wrong 🚫 class House {
  constructor(address) {
    this.address = address;
  }
  address() {
    return this.address;
  }
  openDoor() {
    console.log("Door opened at " + this.address);
  }
}

class Motorhome extends House {
  constructor() {
    super(null);
  }
  address() {
    return null;
    // This implementation is the same as the parent's
    // and is also a refused bequest
  }
  openDoor() {
    console.log("Motorhome door opened.");
  }
} Right 👉 class House {
  constructor(address) {
    this.address = address;
  }
  address() {
    return this.address;
  }
  openDoor() {
    console.log("Door opened at " + this.address);
  }
}

class Motorhome {
  // does not inherit from House
  constructor(gps) {
    this.gps = gps;
  }
  openDoor() {
    console.log("Motorhome door opened at " + this.gps.getLocation());
  }
} Detection 🔍 [x]Manual Look for subclasses that override or ignore most of their parent’s behavior. You should reconsider the inheritance if a subclass sets parent properties to null or reimplements core methods. Tags 🏷️ Inheritance Level 🔋 [x]Intermediate Why the Bijection Is Important 🗺️ Your software should reflect real-world relationships. When you force a subclass that doesn’t logically extend its parent in the Bijection, you mislead developers and introduce maintenance problems. AI Generation 🤖 AI can generate this smell when it defaults to inheritance for reuse instead of composition. This happens when AI follows generic templates without understanding the context. AI Detection 🥃 AI can detect this smell by analyzing class structures and inheritance trees. However, it struggles with subtle cases where inheritance initially seems valid but breaks expectations. Try Them! 🛠 Remember: AI Assistants make lots of mistakes Without Proper Instructions

With Specific Instructions



ChatGPT

ChatGPT



Claude

Claude



Perplexity

Perplexity



Copilot

Copilot



Gemini

Gemini



DeepSeek

DeepSeek



Meta AI

Meta AI Conclusion ✔️ When you design a class hierarchy, you need to make sure that subclasses logically inherit from their parent. If a subclass refuses some of the behavior, you should rethink your design. Relations 👩‍❤️‍💋‍👨 Code Smell 11 - Subclassification for Code Reuse Code Smell 58 - Yo-yo Problem Code Smell 43 - Concrete Classes Subclassified More Information 📕 Refactoring Guru Code Smells Disclaimer 📘 Code Smells are my opinion. Credits 🙏 Photo by Hanson Lu on Unsplash Favor object composition over class inheritance. Erich Gamma Software Engineering Great Quotes This article is part of the CodeSmell Series. How to Find the Stinky Parts of your Code When you ignore your inheritance, you will have trouble with your parents When you ignore your inheritance, you will have trouble with your parents TL;DR: Subclasses should honor ALL their parent’s contract. TL;DR: Subclasses should honor ALL their parent’s contract. Problems 😔 Wrong abstraction Subclassification for code reuse Misleading hierarchy Unused or overridden methods Unnecessary complexity Liskov Principle Violation Maintenanabiilty YoYo Hierachies Concrete classes subclassified Wrong abstraction Subclassification for code reuse Subclassification for code reuse Misleading hierarchy Unused or overridden methods Unnecessary complexity Liskov Principle Violation Maintenanabiilty YoYo Hierachies YoYo Hierachies Concrete classes subclassified Concrete classes subclassified Solutions 😃 Favor composition over inheritance Don't subclassify for code reuse Rethink hierarchy Extract shared logic Use interfaces Remove dead code Favor composition over inheritance Don't subclassify for code reuse code reuse Rethink hierarchy Extract shared logic Use interfaces Remove dead code Refactorings ⚙️ Refactoring 007 - Extract Class Refactoring 007 - Extract Class Context 💬 When you create a subclass, it should use or extend the behavior of its parent. If it ignores or overrides most of it, you probably force inheritance where it doesn’t belong to reuse code. This makes the code misleading and hard to maintain. Sample Code 📖 Wrong 🚫 class House {
  constructor(address) {
    this.address = address;
  }
  address() {
    return this.address;
  }
  openDoor() {
    console.log("Door opened at " + this.address);
  }
}

class Motorhome extends House {
  constructor() {
    super(null);
  }
  address() {
    return null;
    // This implementation is the same as the parent's
    // and is also a refused bequest
  }
  openDoor() {
    console.log("Motorhome door opened.");
  }
} class House {
  constructor(address) {
    this.address = address;
  }
  address() {
    return this.address;
  }
  openDoor() {
    console.log("Door opened at " + this.address);
  }
}

class Motorhome extends House {
  constructor() {
    super(null);
  }
  address() {
    return null;
    // This implementation is the same as the parent's
    // and is also a refused bequest
  }
  openDoor() {
    console.log("Motorhome door opened.");
  }
} Right 👉 class House {
  constructor(address) {
    this.address = address;
  }
  address() {
    return this.address;
  }
  openDoor() {
    console.log("Door opened at " + this.address);
  }
}

class Motorhome {
  // does not inherit from House
  constructor(gps) {
    this.gps = gps;
  }
  openDoor() {
    console.log("Motorhome door opened at " + this.gps.getLocation());
  }
} class House {
  constructor(address) {
    this.address = address;
  }
  address() {
    return this.address;
  }
  openDoor() {
    console.log("Door opened at " + this.address);
  }
}

class Motorhome {
  // does not inherit from House
  constructor(gps) {
    this.gps = gps;
  }
  openDoor() {
    console.log("Motorhome door opened at " + this.gps.getLocation());
  }
} Detection 🔍 [x]Manual [x] Manual [x] Look for subclasses that override or ignore most of their parent’s behavior. You should reconsider the inheritance if a subclass sets parent properties to null or reimplements core methods. Tags 🏷️ Inheritance Inheritance Level 🔋 [x]Intermediate [x] Intermediate [x] Why the Bijection Is Important 🗺️ Your software should reflect real-world relationships. When you force a subclass that doesn’t logically extend its parent in the Bijection , you mislead developers and introduce maintenance problems. Bijection AI Generation 🤖 AI can generate this smell when it defaults to inheritance for reuse instead of composition. This happens when AI follows generic templates without understanding the context. AI Detection 🥃 AI can detect this smell by analyzing class structures and inheritance trees. However, it struggles with subtle cases where inheritance initially seems valid but breaks expectations. Try Them! 🛠 Remember: AI Assistants make lots of mistakes Remember: AI Assistants make lots of mistakes Without Proper Instructions

With Specific Instructions



ChatGPT

ChatGPT



Claude

Claude



Perplexity

Perplexity



Copilot

Copilot



Gemini

Gemini



DeepSeek

DeepSeek



Meta AI

Meta AI Without Proper Instructions

With Specific Instructions ChatGPT

ChatGPT Claude

Claude Perplexity

Perplexity Copilot

Copilot Gemini

Gemini DeepSeek

DeepSeek Meta AI

Meta AI Without Proper Instructions With Specific Instructions Without Proper Instructions Without Proper Instructions With Specific Instructions With Specific Instructions ChatGPT ChatGPT ChatGPT ChatGPT ChatGPT ChatGPT ChatGPT ChatGPT Claude Claude Claude Claude Claude Claude Claude Claude Perplexity Perplexity Perplexity Perplexity Perplexity Perplexity Perplexity Perplexity Copilot Copilot Copilot Copilot Copilot Copilot Copilot Copilot Gemini Gemini Gemini Gemini Gemini Gemini Gemini Gemini DeepSeek DeepSeek DeepSeek DeepSeek DeepSeek DeepSeek DeepSeek DeepSeek Meta AI Meta AI Meta AI Meta AI Meta AI Meta AI Meta AI Meta AI Conclusion ✔️ When you design a class hierarchy, you need to make sure that subclasses logically inherit from their parent. If a subclass refuses some of the behavior, you should rethink your design. Relations 👩‍❤️‍💋‍👨 Code Smell 11 - Subclassification for Code Reuse Code Smell 11 - Subclassification for Code Reuse Code Smell 58 - Yo-yo Problem Code Smell 58 - Yo-yo Problem Code Smell 43 - Concrete Classes Subclassified Code Smell 43 - Concrete Classes Subclassified More Information 📕 Refactoring Guru Refactoring Guru Code Smells Code Smells Disclaimer 📘 Code Smells are my opinion . opinion Credits 🙏 Photo by Hanson Lu on Unsplash Hanson Lu Unsplash Favor object composition over class inheritance. Favor object composition over class inheritance. Erich Gamma Erich Gamma Software Engineering Great Quotes Software Engineering Great Quotes This article is part of the CodeSmell Series. How to Find the Stinky Parts of your Code How to Find the Stinky Parts of your Code

Here's Why You Should Replace Inheritance with Delegation

How to Implement the Visitor Pattern Correctly

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