Behavior is repeated across the system. But you are missing a concept
TL;DR: Put together what belongs together
Code Duplication
Missing Abstraction
Low Cohesion
https://maximilianocontieri.com/code-smell-124-divergent-change
https://maximilianocontieri.com/code-smell-143-data-clumps
https://maximilianocontieri.com/code-smell-147-too-many-methods
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.
Extract the methods (and accidentally the properties) coupled into a new concept
Use the new concept
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; } }
// 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(); } }
[X] Automatic
Most IDEs implement this safe refactor.
This is a safe refactoring.
Logic code is in just one place together with its rules.
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).
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.
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."
[X] Intermediate
https://maximilianocontieri.com/refactoring-002-extract-method
https://maximilianocontieri.com/refactoring-019-reify-email-addresses
https://maximilianocontieri.com/refactoring-013-remove-repeated-code
https://maximilianocontieri.com/refactoring-023-replace-inheritance-with-delegation
https://maximilianocontieri.com/refactoring-018-replace-singleton
https://maximilianocontieri.com/refactoring-020-transform-static-functions
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
https://refactoring.com/catalog/extractClass.html
https://refactoring.guru/extract-class
Image from drpepperscott230 on Pixabay
This article is part of the Refactoring Series
https://maximilianocontieri.com/how-to-improve-your-code-with-easy-refactorings
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