Code Refactor

Process of restructuring existing computer code without changing/breaking its external behavior.

Advantages

• Important step of TDD. Give confidence that code is not broken.
• improved code readability and reduced complexity
• improve the maintainability by making easier to fix bugs
• create a simpler, cleaner, or more expressive internal architecture or object model to improve extensibility.
• improved performance

Steps to Refactor Project

Get Understanding of Code

• Program Dependence Graph - explicit representation of data and control dependencies
• System Dependence Graph - representation of procedure calls between PDG
• Software intelligence - reverse engineers the initial state to understand existing intra-application dependencies

Add Abstraction

• Encapsulate field – force code to access the field with getter and setter methods
• Generalize type – create more general types to allow for more code sharing
• Replace type-checking code in switch with state/strategy of subclass
• Replace conditional with polymorphism of sub class

Break down Code

• 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.

Improve name & location

• Move method or move field – move to a more appropriate class or source file
• Rename method or rename field – changing the name into a new one that better reveals its purpose
• Pull up – in object-oriented programming (OOP), move to a superclass
• Push down – in OOP, move to a subclass
• Automatic duplicate code detection