Refactoring Day 17 : Extract Superclass

Today’s refactoring is from Martin Fowler’s refactoring catalog. You can find the original description here

This refactoring is used quite often when you have a number of methods that you want to “pull up” into a base class to allow other classes in the same hierarchy to use. Here is a class that uses two methods that we want to extract and make available to other classes.

   1: public class Dog

   2: {

   3:     public void EatFood()

   4:     {

   5:         // eat some food

   6:     }

   7:  

   8:     public void Groom()

   9:     {

  10:         // perform grooming

  11:     }

  12: }

After applying the refactoring we just move the required methods into a new base class. This is very similar to the [pull up refactoring], except that you would apply this refactoring when a base class doesn’t already exist.

   1: public class Animal

   2: {

   3:     public void EatFood()

   4:     {

   5:         // eat some food

   6:     }

   7:  

   8:     public void Groom()

   9:     {

  10:         // perform grooming

  11:     }

  12: }

  13:  

  14: public class Dog : Animal

  15: {

  16: }

This is part of the 31 Days of Refactoring series. For a full list of Refactorings please see the original introductory post.