April 2022
Beginner to intermediate
344 pages
9h 32m
Japanese
Content preview from はじめての設計をやり抜くための本 第2版 概念モデリングからアプリケーション、データベース、アーキテクチャ設計、アジャイル開発まで
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287
導
入
編
1
設
計
編
ア
キ
テ
ク
チ
ャ
編
2
3
4
5
6
7
6
依存性の注入（
DI
）
これまでに紹介してきたサブシステム分割やレイヤーなどは、システムの
保守性を高めるためにクラス間の依存関係を整理する手法です。これから説
明するDI（依存性の注入）も、同じようにクラス間の依存関係を整理する
ための手法です。DIもシステムの保守性を高めます。
DIはDependency Injection の略で、日本語では「依存性の注入」と呼ば
れます。DIはクラスの呼び出し元と、呼び出すクラスとの間を疎結合にす
るための仕組みです。
のようなクラス図があるとします。Tunerクラスはラジオのチュー
ナーを表します。Tunerクラスには外部出力としてSpeakerクラスが1 つ付
いています。Tunerクラスがラジオの電波を受信して、Speakerクラスから
音声を出力することができます。もちろん、それ相当のハードウェアと連動
して動くのでしょう。
Tuner
Speaker
1
図
6
-
13
：クラス図の例
さて、このサンプルでは、TunerクラスはSpeakerクラスに直接関連して
います。Tunerクラスは、Speakerクラスと直結していることになります。
スピーカー標準装備のラジオチューナーということです。スピーカー標準装
備はうれしくもあり、邪魔でもあります。スピーカーを外してヘッドホンで
聞きたい場合もあるでしょう。街の中で聞くには、ヘッドホンのほうが音質
288
導
入
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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.