Template Method Pattern

What is Template method pattern?

Template method pattern defines the skeleton of an algorithm in a method, deferring some steps to subclasses. Template method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.

When to use it?

• Use Template method pattern when you have classes that contains similar algorithms with minor differences.

Problem

Let's say we create classes represents animal behavior. Our first version of implementation is below:

1. Animal
   
   Instead of defining doDailyRoutine in subclasses, we define it in superclass Animal. All animals exactly follow the order, that is, wakeUp, eat, sleep. eat method is declared as abstract because each animal eats different things.
   
   additionalBehavior has empty body, so it does nothing. However, we can override the method in subclasses if some animal have unique behavior. This kind of method is called hook in Template method pattern.




2. Animal subclasses
   
   Although animal subclasses can't change algorithm structure, they can override some of the step methods used by doDailyRoutine(). Also, they can optionally add additional behavior by overriding the hook method.

Structure