Template Method Design Pattern

The Template Method Pattern is a behavioral design pattern in object-oriented programming that defines the skeleton of an algorithm in a method in the superclass but lets subclasses override specific steps of the algorithm without changing its structure. In other words, it allows a template algorithm to be defined in a base class, with some steps implemented in the base class and others left to be implemented by subclasses.

key points of the Template Method Design Pattern:

1. Intent:

   • The main intent of the Template Method pattern is to define the skeleton of an algorithm in the superclass but allow subclasses to alter specific steps of the algorithm without changing its structure.

2. Key Components:

   • AbstractClass:
     • Defines the abstract template method that represents the skeleton of the algorithm. It may also include concrete methods and abstract methods that are called within the template method.
   • ConcreteClass:
     • Implements the abstract methods declared in the AbstractClass. It provides specific implementations for the steps of the algorithm.

3. Template Method:

   • The template method is a method in the AbstractClass that defines the algorithm's structure. It calls various steps, some of which may be implemented in the AbstractClass and others left to be implemented by ConcreteClass.

4. Abstract Methods:

   • Abstract methods are declared in the AbstractClass and represent steps of the algorithm that must be implemented by ConcreteClass. These methods are typically marked as abstract and are left for subclasses to implement.

5. Hook Methods:

   • Hook methods are methods declared in the AbstractClass that have default (empty or default) implementations. Subclasses can choose to override these methods if they need to, but it's not required.

6. Common Steps:

   • The template method defines the common steps of the algorithm that are shared across all subclasses, ensuring consistency in the overall process.

7. Advantages:

   • Consistency: It ensures consistency in the algorithm across subclasses.
   • Reuse: Common steps are defined in the template method, promoting code reuse.
   • Flexibility: Subclasses can customize specific steps of the algorithm without changing its structure.

8. Use Cases:

   • The Template Method pattern is useful when there's a common algorithm with some steps that can be implemented differently by subclasses.
   • It is applicable when you want to avoid code duplication by providing a common template for a family of algorithms.

Example:

• Consider a document processing application where you have a template for processing documents that includes steps like opening, editing, saving, and closing. Subclasses for different document types can customize the editing or saving steps.