July 2024
Beginner to intermediate
272 pages
5h 40m
Japanese
Content preview from アーキテクトの教科書 価値を生むソフトウェアのアーキテクチャ構築
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066
局所化されるということです。この例でいうと、
OvertimePay
PolicyFactory
の条件分岐と、
OvertimePayPolicy
の実装クラスのロジッ
クに対してユニットテストを修正すれば、振る舞いの正しさを担保する
ことができます（もちろん、受け入れテストなど上位のテストはまた別
の話です）。
LSP：リスコフの置換原則
派生型はその基本型と置換可能でなければならない。
※7
LSPは、ある基本型を使って処理を記述したどのようなプログラムに
対しても、その振る舞いを変えることなく、基本型を派生型で置き換え
可能でなければならないという原則です。
オブジェクト指向言語の抽象クラスやインターフェースの仕組みを
使って実装していれば一見当たり前のことのようにも思えますが、LSP
に違反してしまうケースも存在するのです。
具体例を見てみましょう。
リスト2.3.6は、チケット管理ツールのコードの一部だと考えてくだ
さい。抽象クラス
Ticket
のサブクラスとして
BugTicket
と
StoryTicket
が存在します。
Ticket
にはポイント数で見積もりを行う
estimate
メソッ
ドがあり、事前条件（メソッドを呼び出す際に成立しているべき条件）
としてポイント数が正の整数であることをアサーション文で宣言してい
ます。Java言語のアサーションは、
assert
キーワードの後ろの
boolean
式を評価し、それが真でない場合は
AssertionError
を送出します。
さて、派生クラスの
StoryTicket ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.