#Template Method
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.
Motivation
Sometimes you want to specify the order of operations that a method uses, but allow subclasses to provide their own implementations of some of these operations
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.
Applicability
- To implement the invariant parts of an algorithm once and leave it up to subclasses to implement the behavior that can vary.
- To localize common behavior among subclasses and place it in a common class (in this case, a superclass) to avoid code duplication. This is a classic example of “code refactoring.”
- To control how subclasses extend superclass operations. You can define a template method that calls "hook" operations at specific points, thereby permitting extensions only at those points. The Template Method is a fundamental technique for code reuse.