Applicability

The Template 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.
• ConcreteClass: implements the primitive operations to carry out subclass-specific steps of the algorithm.

Collaborations

ConcreteClass relies on AbstractClass to implement the invariant steps of the algorithm.

Sample Code

Template Method

Related Patterns

• Factory Methods are often called by template methods.
• Strategy: Template methods use inheritance to vary part of an algorithm. Strategies use delegation to vary the entire algorithm.