Transform your rigid inheritance into flexible delegations TL;DR: Replace restrictive inheritance hierarchies with flexible object delegation Problems Addressed 🤯 Liskov substitution violation
Rigid class hierarchy
Hidden dependencies
Tight Coupling
Limited Reusability
Single Responsibility principle violation Related Code Smells 🧑‍💻 https://hackernoon.com/code-smell-290-refused-bequest?embedable=true https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-iii-t7h3zkv https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xiv https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-vii-8dk31x0 https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxv Steps 🔄 Create a temporary field in the subclass for the superclass.
Update subclass methods to delegate calls.
Add delegation methods for inherited behavior.
Remove inheritance and update object creation. Sample Code 💻 Before 🚨 class Chatbot {    
    public void respond(String question) {
        // Here is the logic to answer a question
    }
}

class Robot extends Chatbot {
    // The Physical Robot inherits the logic
    // to answer questions
    // and adds physical behavior
    public void move() {
        System.out.println("Moving...");
    }
    
    public void grab() {
        System.out.println("Grabbing object...");
    }
} After class Brain {
    public String answer(String question) {
        // The common logic to answer questions
        // is extracted into a different object
        return "Thinking... Answering: " + question;
    }
}

final class Chatbot {    
    private final Brain brain;
    
    Chatbot(Brain brain) {
        this.brain = brain;
    }
    
    public void respond(String question) {
        System.out.println(this.brain.answer(question));
    }
}

final class Robot {
    // 4. Remove inheritance and update object creation.
    private final Brain brain;    
    // 1. Create a temporary field in the subclass for the superclass.
    // private final Chatbot chatbot;  
    
    Robot(Brain brain) {
        this.brain = brain;
        // 2. Update subclass methods to delegate calls.
        // this.chatbot = new Chatbot(brain);
        // This code is removed after step 4
    }
    
    public void move() {
        System.out.println("Moving...");
    }
    
    public void grab() {
        System.out.println("Grabbing object...");
    }
    
    public void respond(String question) {
        // 3. Add delegation methods for inherited behavior.
        // chatbot.respond(question);
        // This code is also removed after step 4 
        System.out.println(this.brain.answer(question));
        // The physical robot can also use it as text-to-speech
    }
} Type 🛠️ Semi-Automatic Safety 🛡️ This refactoring is safe when done carefully and with proper testing. You should ensure all delegated method signatures match exactly and maintain existing behavior. The main risk comes from missing methods that need delegation or incorrectly implementing the delegation methods. Why is the Code Better? ✨ You gain the flexibility to change implementations at runtime and avoid the pitfalls of inheritance like tight coupling. How Does it Improve the Bijection? This refactoring improves the Bijection between code and reality by better modeling real-world relationships. A robot doesn't inherit from a brain in the real world - it has a brain. By replacing inheritance with delegation, you create a more accurate representation of the actual relationship between objects using the MAPPER. Limitations ⚠️ The rewriting requires writing additional delegation methods. If subclass logic relies too much on the superclass, delegation might increase boilerplate. Refactor with AI Without Proper Instructions

With Specific Instructions



ChatGPT

ChatGPT



Claude

Claude



Perplexity

Perplexity



Copilot

Copilot



Gemini

Gemini



DeepSeek

DeepSeek



Meta AI

Meta AI Tags 🏷️ Inheritance Related Refactorings 🔄 https://maximilianocontieri.com/refactoring-007-extract-class?embedable=true See also 📚 https://refactoring.guru/replace-inheritance-with-delegation?embedable=true Credits Image by Gerd Altmann on Pixabay This article is part of the Refactoring Series. https://maximilianocontieri.com/how-to-improve-your-code-with-easy-refactorings?embedable=true Transform your rigid inheritance into flexible delegations Transform your rigid inheritance into flexible delegations TL;DR: Replace restrictive inheritance hierarchies with flexible object delegation TL;DR: Replace restrictive inheritance hierarchies with flexible object delegation Problems Addressed 🤯 Liskov substitution violation Rigid class hierarchy Hidden dependencies Tight Coupling Limited Reusability Single Responsibility principle violation Liskov substitution violation Rigid class hierarchy Hidden dependencies Tight Coupling Coupling Limited Reusability Single Responsibility principle violation Related Code Smells 🧑‍💻 https://hackernoon.com/code-smell-290-refused-bequest?embedable=true https://hackernoon.com/code-smell-290-refused-bequest?embedable=true https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-iii-t7h3zkv https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-iii-t7h3zkv https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xiv https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xiv https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-vii-8dk31x0 https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-vii-8dk31x0 https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxv https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxv Steps 🔄 Create a temporary field in the subclass for the superclass. Update subclass methods to delegate calls. Add delegation methods for inherited behavior. Remove inheritance and update object creation. Create a temporary field in the subclass for the superclass. Update subclass methods to delegate calls. Add delegation methods for inherited behavior. Remove inheritance and update object creation. Sample Code 💻 Before 🚨 class Chatbot {    
    public void respond(String question) {
        // Here is the logic to answer a question
    }
}

class Robot extends Chatbot {
    // The Physical Robot inherits the logic
    // to answer questions
    // and adds physical behavior
    public void move() {
        System.out.println("Moving...");
    }
    
    public void grab() {
        System.out.println("Grabbing object...");
    }
} class Chatbot {    
    public void respond(String question) {
        // Here is the logic to answer a question
    }
}

class Robot extends Chatbot {
    // The Physical Robot inherits the logic
    // to answer questions
    // and adds physical behavior
    public void move() {
        System.out.println("Moving...");
    }
    
    public void grab() {
        System.out.println("Grabbing object...");
    }
} After class Brain {
    public String answer(String question) {
        // The common logic to answer questions
        // is extracted into a different object
        return "Thinking... Answering: " + question;
    }
}

final class Chatbot {    
    private final Brain brain;
    
    Chatbot(Brain brain) {
        this.brain = brain;
    }
    
    public void respond(String question) {
        System.out.println(this.brain.answer(question));
    }
}

final class Robot {
    // 4. Remove inheritance and update object creation.
    private final Brain brain;    
    // 1. Create a temporary field in the subclass for the superclass.
    // private final Chatbot chatbot;  
    
    Robot(Brain brain) {
        this.brain = brain;
        // 2. Update subclass methods to delegate calls.
        // this.chatbot = new Chatbot(brain);
        // This code is removed after step 4
    }
    
    public void move() {
        System.out.println("Moving...");
    }
    
    public void grab() {
        System.out.println("Grabbing object...");
    }
    
    public void respond(String question) {
        // 3. Add delegation methods for inherited behavior.
        // chatbot.respond(question);
        // This code is also removed after step 4 
        System.out.println(this.brain.answer(question));
        // The physical robot can also use it as text-to-speech
    }
} class Brain {
    public String answer(String question) {
        // The common logic to answer questions
        // is extracted into a different object
        return "Thinking... Answering: " + question;
    }
}

final class Chatbot {    
    private final Brain brain;
    
    Chatbot(Brain brain) {
        this.brain = brain;
    }
    
    public void respond(String question) {
        System.out.println(this.brain.answer(question));
    }
}

final class Robot {
    // 4. Remove inheritance and update object creation.
    private final Brain brain;    
    // 1. Create a temporary field in the subclass for the superclass.
    // private final Chatbot chatbot;  
    
    Robot(Brain brain) {
        this.brain = brain;
        // 2. Update subclass methods to delegate calls.
        // this.chatbot = new Chatbot(brain);
        // This code is removed after step 4
    }
    
    public void move() {
        System.out.println("Moving...");
    }
    
    public void grab() {
        System.out.println("Grabbing object...");
    }
    
    public void respond(String question) {
        // 3. Add delegation methods for inherited behavior.
        // chatbot.respond(question);
        // This code is also removed after step 4 
        System.out.println(this.brain.answer(question));
        // The physical robot can also use it as text-to-speech
    }
} Type 🛠️ Semi-Automatic Semi-Automatic Safety 🛡️ This refactoring is safe when done carefully and with proper testing. You should ensure all delegated method signatures match exactly and maintain existing behavior. The main risk comes from missing methods that need delegation or incorrectly implementing the delegation methods. Why is the Code Better? ✨ You gain the flexibility to change implementations at runtime and avoid the pitfalls of inheritance like tight coupling. How Does it Improve the Bijection? This refactoring improves the Bijection between code and reality by better modeling real-world relationships. Bijection A robot doesn't inherit from a brain in the real world - it has a brain. By replacing inheritance with delegation, you create a more accurate representation of the actual relationship between objects using the MAPPER . MAPPER Limitations ⚠️ The rewriting requires writing additional delegation methods. If subclass logic relies too much on the superclass, delegation might increase boilerplate. Refactor with 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 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 Tags 🏷️ Inheritance Inheritance Related Refactorings 🔄 https://maximilianocontieri.com/refactoring-007-extract-class?embedable=true https://maximilianocontieri.com/refactoring-007-extract-class?embedable=true See also 📚 https://refactoring.guru/replace-inheritance-with-delegation?embedable=true https://refactoring.guru/replace-inheritance-with-delegation?embedable=true Credits Image by Gerd Altmann on Pixabay Gerd Altmann Pixabay This article is part of the Refactoring Series. https://maximilianocontieri.com/how-to-improve-your-code-with-easy-refactorings?embedable=true https://maximilianocontieri.com/how-to-improve-your-code-with-easy-refactorings?embedable=true

Changing Keys, Losing Values

Code Smell 290 - Refused Bequest

Buy My Book

Share your ideas with me!

Here's Why You Should Replace Inheritance with Delegation

About Author

Comments

TOPICS

THIS ARTICLE WAS FEATURED IN

Related Stories

10 Predictions About the Future of Finance

106 Stories To Learn About Clean Code

100 Pieces of Programming Advice from the Book Clean Code by Robert Martin

110 Stories To Learn About Refactoring

3 Things Coding And Prose Writing Have In Common According To Cory House

4 Simple Habits For Engineering Teams To Beat Technical Debt

10 Predictions About the Future of Finance

106 Stories To Learn About Clean Code

100 Pieces of Programming Advice from the Book Clean Code by Robert Martin

110 Stories To Learn About Refactoring

3 Things Coding And Prose Writing Have In Common According To Cory House

4 Simple Habits For Engineering Teams To Beat Technical Debt

Light-Mode

Classic

Newspaper

Minty

Dark-Mode

Neon Noir

Minty

HN StartUps