学习笔记：Legacy code refactor

1 code refactor的定义：

Code refactoring is the process of restructuring existing computer code - changing the factoring- without changing its external behavior. Refactoring improves nonfunctional attributes of the software. Advantages include improved code readability and reduced complexity to improve source code maintainability, and create a more expressive internal architecture or object model to improve extensibility.

关键词：对当前code结构等额重新调整，不改变code本身的外部行为，非功能性的调整，可以从可读性，复杂度，可维护性等方面进行调整。

code refactor能够带来的好处：

主要体现在两个方面：可维护性，可扩展性

code refactor的过程：是一个迭代的过程，小范围的改变，测试确保正确性之后再修改测试。在refactor的过程中单元测试是非常必要的，它可以用来验证failure是由于原来的代码本身有问题还是因为refactor造成的。

常用的refactor技术：

1）更高的抽象：

# Encapsulate Field \u2013 force code to access the field with getter and setter methods（用getter、setter来对属性进行封装）
# Generalize Type \u2013 create more general types to allow for more code sharing
# Replace type-checking code with State/Strategy[5]（对类型的检查的code可以使用状态或者策略模式）
# Replace conditional with polymorphism （使用多态来代替条件）

2）对code进行逻辑上更小的分片

    * Componentization breaks code down into reusable semantic units that present clear, well-defined, simple-to-use interfaces.
    * Extract Class moves part of the code from an existing class into a new class.
    * Extract Method, to turn part of a larger method into a new method. By breaking down code in smaller pieces, it is more easily understandable. This is also applicable to functions.

3）code的名称和位置：

    * Move Method or Move Field \u2013 move to a more appropriate Class or source file
    * Rename Method or Rename Field \u2013 changing the name into a new one that better reveals its purpose
    * Pull Up \u2013 in OOP, move to a superclass （讲子类的方法移到父类）
    * Push Down \u2013 in OOP, move to a subclass（将父类的方法移到子类）

一些建议：

Most re-factoring is done to 'make maintenance and future development easier'；

But for each re-factor made we can justify 'this specific change will make the actual task we are doing now easier'. Rather than 'this is now cleaner for future work'.