template-method

Template Method Pattern

Intent

Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefinecertain steps of an algorithm without changing the algorithm's structure.

Applicability

The Template Method pattern should be used

• to implement the invariant parts of an algorithm once and leave it up to subclasses to implement the behavior that can vary.
• when common behavior among subclasses should be factored and localized in a common class to avoid code duplication.
• to control subclasses extensions. You can define a template method that calls "hook" operations at specific points,thereby permitting extensions only at those points.

Structure

Participants

• AbstractClass
  • defines abstract primitive operations that concrete subclasses define to implement steps of an algorithm.
  • implements a template method defining the skeleton of an algorithm.The template method calls primitive operations as well as operations defined in AbstractClass or those of other objects.
• ConcreteClass
  • implements the primitive operations to carry out subclass-specific steps of the algorithm.

Example

Imagine a customer go to a restaurant, the common action of customers is ordering some food and then giving some comments. We can create a template for customers' action pattern, and let specific customer determine what specific operation they want to do.

Participants in this example:

• Customer is the AbstractClass.
• Vegan/MeatLover is the ConcreteClass.

Scala Tips

N/A

Reference

• Design Patterns: Elements of Reusable Object-Oriented Software