[JAVA] Knowledge required for object-oriented refactoring

Introduction

We will continue to add things that we think are necessary for refactoring in Java. The books I referred to are as follows.

• Hiroshi Yuki, "Introduction to Refactoring Learned in the Java Language", published by Softbank Creative Co., Ltd.
• Dustin Boswell, Trevor Foucher, "Readable Code", published by O'Reilly Japan
• Akira Hirasawa, "Why make it object-oriented", published by Nikkei BP

Principles to be aware of

--DRY (Do n’t Repeat Your Self) Principle

• https://ja.wikipedia.org/wiki/Don%27t_repeat_yourself --Avoid repetition (duplicate) --KISS (Keep it simple, stupid) principle
• https://ja.wikipedia.org/wiki/KISS%E3%81%AE%E5%8E%9F%E5%89%87 --Design simplicity is important, and unnecessary complexity should be avoided --YAGNI (You ain't gonna need it) Principle
• https://ja.wikipedia.org/wiki/YAGNI --Features should not be added until they are actually needed

Prerequisite knowledge

--Basic understanding of OOP (Object Oriented Programming) --Relationship between class and instance --Access modifier --Inheritance (abstract classes and interfaces) --Override, overload --Local variables, instance variables, static variables (class variables)

Definition of refactoring

• Improving the internal structure of a program without changing the behavior of the program as seen from the outside

About the test

• Must have a unit test

Unit test definition

• Created by the developer himself
• Targeting code (usually a unit of class or method)
• Must be automated

Purpose of refactoring

• Make it easier to find bugs
• Make it easier to add features
• Make it easier to review

Tips

• Follow the refactoring catalog instead of fixing it with the senses
• Step by step (one at a time)
• First, sniff out the ominous smell

Ominous odor (possibility of refactoring)

An ominous odor is the part of the code that needs to be refactored. The scent is a knack for sensuously feeling the "difficult to understand," "difficult to modify," and "difficult to expand" parts of a program.

See List of "Ominous Smell" Suggesting Refactoring Possibility

Refactoring Catalog

"Refactoring" by Martin Fowler A catalog of refactoring methods published by ThoughtWorks, to which

• https://refactoring.com/catalog/

A partial excerpt from a frequently-used catalog See Refactoring Catalog (Excerpt)