Refactoring Day 4 : Push Down Method

Yesterday we looked at the pull up refactoring to move a method to a base class so mutiple derived classes 
can use a method. Today we look at the opposite. Here is the code before the refactoring: 
 1: public abstract class Animal 
 2: { 
 3: public void Bark() 
 4: { 
 5: // code to bark 
 6: } 
 7: } 
 8: 
 9: public class Dog : Animal 
 10: { 
 11: } 
 12: 
 13: public class Cat : Animal 
 14: { 
 15: } 
 
So here we have some code with a base class that has a Bark method. Perhaps at one time our cat could 
bark, but now we no longer need that functionality on the Cat class. So we “Push Down” the Bark method 
into the Dog class as it is no longer needed on the base class but perhaps it is still needed when dealing 
explicitly with a Dog. At this time, it’s worthwhile to evaluate if there is any behavior still located on the 
Animal base class. If not, it is a good opportunity to turn the Animal abstract class into an interface instead 
as no code is required on the contract and can be treated as a marker interface. 
 1: public abstract class Animal 
 2: { 
 3: } 
 4: 
 5: public class Dog : Animal 
 6: { 
 7: public void Bark() 
 8: { 
 9: // code to bark 
 10: } 
 11: } 
 12: 
 13: public class Cat : Animal 
 14: { 
 15: }