Comparison

OSS vs Java SE 21 Developer

Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.

Head to head
About

OSS

Features
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【OSS-DB Silver 合格対策の決定版アプリ登場!PostgreSQLの知識をスマホで効率学習】 OSS-DB Silver 試験に挑戦される皆様に向けた、PostgreSQL対応の本格問題集アプリです。本アプリは、OSS-DB Silver(オープンソースデータベース技術者認定資格)の出題範囲を徹底分析し、全10章・210問以上の問題を収録。スキマ時間でも学習が進められるよう、使いやすさと実践力を追求しました。 買い切り型で広告表示なし・ユーザー登録不要。すぐに学習を始められ、全機能が利用可能です。 ■アプリの主な特徴 ・OSS-DB Silver 試験範囲の問題を210問以上収録 ・全10章の単元構成で、段階的に理解を深められる ・1問ごとに丁寧な解説付きで、知識の定着をサポート ・スキマ時間でも学習できるシンプル設計&スマホ最適化 ・試験本番を意識した4択問題で実戦力アップ ■便利で豊富な学習支援機能 本アプリは、学習効率と継続を支えるために以下の機能を搭載しています。 ・回答結果リセット:過去の履歴をクリアして再スタート可能 ・ブックマークリセット:重要問題を一括管理 ・出題順ランダム化:覚えに頼らない本質理解へ ・選択肢ランダム化:選択位置依存を防止 ・間違えた問題だけ再出題:弱点補強に最適 ・ブックマークした問題だけ出題:重要問題を集中復習 ・ランダム出題(5〜50問):空き時間に最適な分量を選択 ・学習進捗の可視化:各単元ごとの達成率を確認 ・ダークモード対応:夜間学習にも最適 ■収録単元(全10章) 本アプリは、公式出題範囲に準拠し、以下の章構成で学習を進められます。 一般知識 データベースの基礎知識 インストール 標準付属ツール 設定ファイル バックアップとリストア 基本的な運用管理 SQLとオブジェクト 組み込み関数と演算子 トランザクション ■OSS-DB Silverとは? OSS-DB Silverは、LPI-Japanが認定するPostgreSQLの技術力を測る国家級資格です。オープンソースデータベース技術の基本から応用までを問う内容で、特にPostgreSQLに関する以下の知識が問われます。 ・データベースの基礎知識 ・インストール・設定ファイルの管理 ・標準ツールの使い方 ・バックアップ・リストアの手法 ・運用管理・権限設定 ・SQLとオブジェクト操作 ・トランザクションとロール管理 難易度は中級程度ですが、未経験者にとっては独学が難しい試験とも言われています。本アプリは、そんな方でも安心して対策できるように設計されています。 ■おすすめの活用シーン ・通勤・通学の電車内で ・お昼休みに5問だけ ・就寝前の復習タイムに ・紙の参考書を開けないスキマ時間に ■無料で試したい方へ まずは試してみたい方向けに、LINE公式アカウントに登録すると無料でサンプル問題が体験可能です。 お気軽に下記リンクよりご利用ください。 https://lin.ee/5aFjAd4 ■インストールして、合格への第一歩を! 独学でも合格できる! このアプリが、あなたのOSS-DB Silver合格の心強いパートナーとなります。 今すぐインストールして、未来のキャリアに繋がる一歩を踏み出しましょう!

About

Java SE 21 Developer

Features
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Keep studying across your phone, tablet and desktop. Use your phone on the move and a tablet or desktop when you want more room to study. Connect the same StudyCert account to continue your learning in the app and on the desktop web. Prepare for Oracle Java SE 21 / 1Z0-830 with 500 practice questions and 149 key terms. Study coverage · 10 areas • Handling Date, Time, Text, Numeric and Boolean Values • Controlling Program Flow • Using Object-Oriented Concepts in Java • Handling Exceptions • Working with Arrays and Collections • Working with Streams and Lambda expressions • Packaging and Deploying Java Code • Managing Concurrent Code Execution • Using Java I/O API • Implementing Localization 1. Build your foundation with key terms Use flashcards to learn meanings, exam context and selection cues. Mark terms as known or not yet known, then revisit unstudied or unfamiliar cards. Edit card content to suit your learning and restore the original when needed. 2. Practice and understand each answer Study in 50-question sets, by domain or by difficulty. Work through single- and multiple-choice questions, then read the explanation for the answer and each option. Choose all, unfinished or wrong questions; shuffle questions and choices; use a study timer; and resume where you left off. From the results of domain study, continue with key terms and related questions in the next domain. 3. Review mistakes and uncertain concepts Choose recent errors, review marks or repeated mistakes on the Review screen and practice them again. Check accuracy by domain alongside the terms you know or still need to learn. The glossary report shows term-learning status and accuracy on related questions together. 4. Check your preparation with a mock exam Practice time management with 50 questions in 120 minutes. Change answers before submission, resume a saved exam and receive grading when time expires. Afterwards, see correct, wrong and unanswered counts, your score and domain results, then revisit mistakes. This practice feature uses the included questions and does not determine an official exam score or pass result. Tools that fit your study routine Optional audio study reads terms and meanings aloud. Choose whether to include exam context and selection cues, set repeats and pauses, and control playback with the mini player. In the mobile app, audio can continue in the background and with the screen locked. A study calendar, learning streaks, weekly goals, reminders for unmet goals and light, dark or system themes support your routine. Learning records are managed for each supported language. Some features require paid access. Check the included features and price on the purchase screen. Purchase restoration is supported. This is an independent study aid, not an official, affiliated or endorsed app of any exam administrator or certification body. Exam names and trademarks belong to their respective owners.

Screenshots

OSS4 screens
Java SE 21 Developer4 screens

Verdict

The call

The clearest difference is price: Java SE 21 Developer at Free against OSS's $3.99. Java SE 21 Developer also leads on update cadence (weekly vs every 15 months). OSS's advantage is in-app purchases (none vs 1). On ads, device support and iOS requirement there is nothing between them.

Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS

CostPrice · In-app purchases · Ads · Monetization

Java SE 21 Developer is free to download; OSS costs $3.99 up front. Java SE 21 Developer sells 1 one-off in-app purchase. OSS asks for nothing beyond the download.

UpkeepUpdate frequency

OSS ships an update every 15 months, Java SE 21 Developer weekly. The most recent releases landed on November 5, 2026 and November 13, 2026 respectively.

Scorecard3 real differences · 3 level
OSS versus Java SE 21 Developer: the parameters behind the verdict, then further details
ParameterOSSJava SE 21 Developer
Price$3.99Free — better
Update frequencyEvery 15 monthsWeekly — better
AdsNoNo
In-app purchasesNo — betterYes
DevicesiPhone, iPad, iPodiPhone, iPad, iPod
Requires iOS15.115.1
Further details — not scored
Size44 MB233 MB
Age rating4+4+
DeveloperDaisuke MatsubaraCHOI SEONGMIN

In-app purchases

None

OSS

No in-app purchases

1 purchases

Java SE 21 Developer

One-time1
  • Lifetime Access$4.99

Questions

Is OSS free?
OSS costs $3.99, with no in-app purchases.
Is Java SE 21 Developer free?
Java SE 21 Developer is free to download, with in-app purchases available.
Do OSS or Java SE 21 Developer have ads?
Neither OSS nor Java SE 21 Developer shows ads.
Which is updated more often, OSS or Java SE 21 Developer?
OSS ships an update every 15 months, and Java SE 21 Developer weekly. Most recently, OSS was updated on November 5, 2026 and Java SE 21 Developer on November 13, 2026.

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