一.什么是重构？
A series of small steps, each of which changes the program’s internal structure without changing its external behavior。
重构是一系列的小部骤,每一步只修改程序的内部结构,但是不改变它的外部行为.
二.为什么要重构
- To improve the software design
- 为了提高软件设计
-Combat's "it rot"
抵抗代码的腐化
-Makes the program easier to change
使程序更容易修改
- To make the software easier to understand
- 使软件更容易理解
-Write for people, not the compiler
程序是写给人看的,不是给编译器看的.
-Understand unfamiliar code
理解不熟悉的代码
- To help find bugs
- 帮助找到bug
-Refactor while debugging to clarify the code
在为了理清代码而DEBUG时,进行重构.
三.我们应该在什么时候重构?
- To add new functionality
- 添加新的功能时
-Refactor existing code until you understand it
重构现有的代码直到你理解它们
-Refactor the design to make it easy to add
重构设计使它容易添加新的功能
-Refactor to understand the code
重构直到你理解代码
-Rmmediate effect of code review
-Allows for higher level suggestions
Don’t set aside time for refactoring,include it in your normal activities
在日常活动中进行重构,而不是另外找时间去重构.
四.最后的思想
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The one benefit of objects is that they make it easier to change.
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有一个好处就是使得对象更容易修改.
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Refactoring allows you to improve the design after the code is written
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重构允许你在代码已经写完后改进自己的设计.
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Up front design is still important,but not so critical
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事先的设计仍然是很重要的,但是并不那么关键了.
五.例子中用到的的重构条目:
Find temp with a single assignment
Extract Right Hand Side of assignment
Replace all references of temp with new method
Remove declaration and assignment of temp
Compile and test
Create method named after intention of code
Copy extracted code
Look for local variables and parameters
Turn into parameter
Turn into return value
Declare within method
Compile
Replace code fragment with call to new method
Compile and test
Declare method in target class
Copy and fit code
Set up a reference from the source object to the target
Turn the original method into a delegating method
-amountOf(Rental each) {return each.charge()}
-Check for overriding methods
Compile and test
Find all users of the method
-Adjust them to call method on target
Remove original method
Compile and test
Create a new state class for the type code
Add subclasses of the state object, one for each type code
Create an abstract query in the superclass to return the type code. Override in subclasses to return correct type code
Compile
Create field in old class for the state object
Change the type code query to delegate to the state object
Change the type code setting methods to assign an instance of the subclass
Compile and test
Move switch to superclass of inheritance structure
Copy one leg of case statement into subclass
Compile and test
Repeat for all other legs
Replace case statement with abstract method
Take two methods with similar overall structure but varying pieces
Use subclasses of current class, or create a strategy and move the methods to the strategy
At each point of variation extract methods from each source with the the same signature but different body
Declare signature of extracted method in superclass and place varying bodies in subclasses
When all points of variation have been removed,move one source method to superclass and remove the other
六.例子中提到的模式:
策略模式
模版方法模式
状态模式