The 'Gang of Four' Companion:

Template Method Design Pattern

Formal specification of design patterns in LePUS3 and Class-Z

This page is part of the The 'Gang of Four' Companion dedicated to the formal specification in LePUS3 and Class-Z of patterns from the 'Gang of Four' catalogue [Gamma et al 1995].

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The Template Method design motif

The informal description: Excerpts from [Gamma et al. 1995] (adapted for this purpose):

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

Structure: Original OMT diagram converted to UML (Why and How?):

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.

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