[Design Pattern] Template Method Pattern

The Template Method Pattern defines the skeleton of an algorithm in a method, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.

 一. 基本的 Template Method Pattern 示例：

 

二. Template Method Pattern with hook  示例 ：

 

三.  Hook 示例：

 

四.  使用 Hook ：

 

Template Method Pattern 概要： 

Ø         A "template method" defines the steps of an algorithm, deferring to subclasses for the implementation of those steps.

 

Ø         The Template Method gives up an important technique for code reuse.

 

Ø         The template method's abstract class may define concrete classes, abstract classes and hooks.

 

Ø         Abstract methods are implemented by subclasses.

 

Ø         Hooks are methods that do nothing or default behavior in the abstract classes, but may be overridden in the subclass.

 

Ø         To prevent subclasses from changing the algorithm in the template method, declare the template method as final.

 

Ø         The Hollywood Principle guides us to put decision-making in high-level modules that can decide how and when to call low-level modules.

 

Ø         You'll see lots of uses of the Template Method Pattern in real world code, but don't expect it all (like any pattern) to be designed "by the book".

 

Ø         The strategy and Template Method Patterns both encapsulate algorithms, one by inheritance and one by composition.

 

Ø         The Factory Method pattern is a specialization of Template Method.

 

 

 

摘自 Head First Design Patterns, O' REILLY