Behavior is repeated across the system. But you are missing a concept Behavior is repeated across the system. But you are missing a concept TL;DR: Put together what belongs together TL;DR: Put together what belongs together Problems Addressed 😔 Code Duplication
Missing Abstraction
Low Cohesion Code Duplication Missing Abstraction Low Cohesion Related Code Smells 💨 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 https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxix https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxix https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxx https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxx Context 💬 When a class starts doing work that should be delegated to others, it suffers from Low Cohesion. You often see this through "Data Clumps"—groups of variables that always travel together—or methods that seem unrelated to the class's primary responsibility. This bloat makes the code harder to understand and creates a "God Object" that changes for too many different reasons. You need to extract these related behaviors and properties into a new, dedicated class, you give a name to a previously hidden concept. This not only promotes code reuse across the system but also ensures that each class has a single, well-defined reason to change. You are not just moving code; you are discovering the missing abstractions in your domain model. Steps 👣 Extract the methods (and accidentally the properties) coupled into a new concept
Use the new concept Extract the methods (and accidentally the properties) coupled into a new concept Use the new concept Sample Code 💻 Before 🚨 final class Person {

      private String name;

      // Below cohesive properties
      private String homeAreaCode;
      private String homeNumber;

      public String name() {
          return name;
      }

      // Below cohesive behavior
      public String telephoneNumber() {
          return ("(" + homeAreaCode + ") " + homeNumber);
      }
      String areaCode() {
          return homeAreaCode;
      }
      String officeNumber() {
          return officeNumber;
      } 
 } final class Person {

      private String name;

      // Below cohesive properties
      private String homeAreaCode;
      private String homeNumber;

      public String name() {
          return name;
      }

      // Below cohesive behavior
      public String telephoneNumber() {
          return ("(" + homeAreaCode + ") " + homeNumber);
      }
      String areaCode() {
          return homeAreaCode;
      }
      String officeNumber() {
          return officeNumber;
      } 
 } After 👉 // 1. Extract the methods (and accidentally the properties) 
// coupled into a new concept      
   public class TelephoneNumber {

      private String number;
      private String areaCode;

      public String telephoneNumber() {
          return ("(" + areaCode + ") " + number);
      }
      public String areaCode() {
          return areaCode;
      }
      public String number() {
          return number;
      }
   }

final class Person {

      private String name;

      // 2. Use the new concept
      private TelephoneNumber officeTelephone = new TelephoneNumber();

      public String name() {
          return name;
      }
      public String telephoneNumber() {
          return officeTelephone.getTelephoneNumber();
      }

  } // 1. Extract the methods (and accidentally the properties) 
// coupled into a new concept      
   public class TelephoneNumber {

      private String number;
      private String areaCode;

      public String telephoneNumber() {
          return ("(" + areaCode + ") " + number);
      }
      public String areaCode() {
          return areaCode;
      }
      public String number() {
          return number;
      }
   }

final class Person {

      private String name;

      // 2. Use the new concept
      private TelephoneNumber officeTelephone = new TelephoneNumber();

      public String name() {
          return name;
      }
      public String telephoneNumber() {
          return officeTelephone.getTelephoneNumber();
      }

  } Type 📝 [X] Automatic Most IDEs implement this safe refactor. Safety 🛡️ This is a safe refactoring. Why is the Code Better? ✨ Logic code is in just one place together with its rules. How Does it Improve the Bijection? 🗺️ In many software models, you often leave concepts homeless, scattering their behavior and data across unrelated classes. This creates a gap between the Real World (where a concept clearly exists) and the MAPPER (where it is missing). MAPPER When you extract a class, you reify a concept. You give a name and a physical place to an idea that was previously hidden in the implementation details. This direct 1:1 Bijection between a real-world entity and a software object reduces cognitive load. Bijection You no longer need to mental map data clumps back to their original meaning. You are not just organizing code; you are making the software more "real." Tags 🏷️ Hierarchies Hierarchies Level 🔋 [X] Intermediate Related Refactorings 🔄 https://hackernoon.com/improving-the-code-one-line-at-a-time https://hackernoon.com/improving-the-code-one-line-at-a-time https://hackernoon.com/refactoring-019-how-to-reify-email-addresses https://hackernoon.com/refactoring-019-how-to-reify-email-addresses https://hackernoon.com/refactoring-013-eliminating-repeated-code-with-dry-principles https://hackernoon.com/refactoring-013-eliminating-repeated-code-with-dry-principles https://hackernoon.com/heres-why-you-should-replace-inheritance-with-delegation https://hackernoon.com/heres-why-you-should-replace-inheritance-with-delegation https://hackernoon.com/refactoring-018-how-to-replace-a-singleton https://hackernoon.com/refactoring-018-how-to-replace-a-singleton https://hackernoon.com/refactoring-020-transform-static-functions https://hackernoon.com/refactoring-020-transform-static-functions Refactor with AI 🤖 Suggested Prompt: 1. Identify classes with low cohesion and unrelated methods.2. Extract related behaviors and properties into new classes.3. Refactor the original class to use the new extracted classes Suggested Prompt: 1. Identify classes with low cohesion and unrelated methods.2. Extract related behaviors and properties into new classes.3. Refactor the original class to use the new extracted classes Without Proper Instructions 📵 ChatGPT
Claude
Perplexity
Copilot
You
Gemini
DeepSeek
Meta AI
Grok
Qwen ChatGPT ChatGPT Claude Claude Perplexity Perplexity Copilot Copilot You You Gemini Gemini DeepSeek DeepSeek Meta AI Meta AI Grok Grok Qwen Qwen With Specific Instructions 👩‍🏫 ChatGPT
Claude
Perplexity
Copilot
You
Gemini
DeepSeek
Meta AI
Grok
Qwen ChatGPT ChatGPT Claude Claude Perplexity Perplexity Copilot Copilot You You Gemini Gemini DeepSeek DeepSeek Meta AI Meta AI Grok Grok Qwen Qwen See also 📚 https://refactoring.com/catalog/extractClass.html?embedable=true https://refactoring.com/catalog/extractClass.html?embedable=true https://refactoring.guru/extract-class?embedable=true https://refactoring.guru/extract-class?embedable=true Credits 🙏 Image from drpepperscott230 on Pixabay drpepperscott230 Pixabay This article is part of the Refactoring Series https://maximilianocontieri.com/how-to-improve-your-code-with-easy-refactorings https://maximilianocontieri.com/how-to-improve-your-code-with-easy-refactorings

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