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Changes the description of the template method pattern (as discussed in Issue1099) #1101

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Merged
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Nov 19, 2019
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Changes the description of the template method pattern (as discussed in Issue1099) #1101

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735b44b
Declares the template methods as final
dgruntz Nov 17, 2019
2f6a2f1
Extends the description of the template method pattern
dgruntz Nov 17, 2019
66327b0
Removes the final declarations (this was done in another branch)
dgruntz Nov 17, 2019
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9 changes: 7 additions & 2 deletions template-method/README.md
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Expand Up @@ -15,18 +15,23 @@ 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.

To make sure that subclasses don’t override the template method, the template method should be declared `final`.

![alt text](./etc/template-method_1.png "Template Method")

## 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. This is good example of "refactoring to generalize" as described by Opdyke and Johnson. You first identify the differences in the existing code and then separate the differences into new operations. Finally, you replace the differing code with a template method that calls one of these new operations
* to control subclasses extensions. You can define a template method that calls "hook" operations at specific points, thereby permitting extensions only at those points

## Tutorial
* [Template-method Pattern Tutorial](https://www.journaldev.com/1763/template-method-design-pattern-in-java)

## Credits
## Real world examples
* [javax.servlet.GenericServlet.init](https://jakarta.ee/specifications/servlet/4.0/apidocs/javax/servlet/GenericServlet.html#init--):
Method `GenericServlet.init(ServletConfig config)` calls the parameterless method `GenericServlet.init()` which is intended to be overridden in subclasses.
Method `GenericServlet.init(ServletConfig config)` is the template method in this example.

## Credits
* [Design Patterns: Elements of Reusable Object-Oriented Software](http://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/dp/0201633612)