Refactoring 007 — Extract Class

Behavior is repeated across the system. But we are missing a concept

TL;DR: Put together what belongs together

Problems Addressed

• Code Duplication
• Missing Abstraction
• Low Cohesion

Related Code Smells

Code Smell 124 — Divergent Change

Code Smell 143 — Data Clumps

Steps

1. Extract the methods (and accidentally the properties) coupled into a new concept
2. 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 behaviour
      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();
      }
  }

Type

[X] Automatic

Most IDEs like IntelliJIDEA and Eclipse implement this safe refactor.

Why code is better?

Logic code is in just one place together with its rules

Tags

• Classes

See also

Refactoring.com

Refactoring Guru

Refactoring courses

Credits

Image from drpepperscott230 on Pixabay

This article is part of the Refactoring Series.