Usage
The template method is used in frameworks, where each implements the invariant parts of a domain's architecture, leaving "placeholders" for customisation options. This is an example for inversion of control, also called the Hollywood principle. Reasons to use the template method are to
- let subclasses implement (through method overriding) behavior that can vary
- avoid duplication in the code: the general workflow structure is implemented once in the abstract class's algorithm, and necessary variations are implemented in each of the subclasses.
- control at what point(s) subclassing is allowed. As opposed to a simple polymorphic override, where the base method would be entirely rewritten allowing radical change to the workflow, only the specific details of the workflow are allowed to change.
The control structure (inversion of control) that is the result of the application of a template pattern is often referred to as the Hollywood Principle: "Don't call us, we'll call you." Using this principle, the template method in a parent class controls the overall process by calling subclass methods as required. This is shown in the following Java example:
Read more about this topic: Template Method Pattern
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