An Android flashcard app with spaced repetition (SM-2 algorithm) for efficient long-term memorization.

• 📇 Multiple decks — organize cards by subject (languages, biology, programming, etc.)
• 🧠 SM-2 spaced repetition algorithm — the same algorithm used by Anki, schedules each card for review at optimal intervals based on user performance
• 📊 Statistics dashboard — track day streak, retention rate, total reviews, and a 7-day activity chart
• 🎨 Material Design 3 — modern, clean UI with proper theming and accessibility support
• 💾 Offline-first — all data stored locally in SQLite, no internet required
• 🚀 Lightweight — small APK size, no third-party charting libraries (custom BarChartView)

Home	Study Session	Statistics

The project follows a clean, layered architecture:

app/src/main/java/com/example/studybuddy/
├── MainActivity.java         ← decks list (entry point)
├── DeckActivity.java         ← cards inside a deck
├── StudyActivity.java        ← study session with SRS grading
├── AddCardActivity.java      ← create / edit card form
├── StatsActivity.java        ← statistics dashboard
├── model/                    ← POJOs: Deck, Card, ReviewLog
├── database/                 ← SQLiteOpenHelper + Repository pattern
├── adapter/                  ← RecyclerView adapters
└── util/
    ├── SpacedRepetition.java ← SM-2 algorithm implementation
    └── BarChartView.java     ← custom View for the 7-day chart

• Repository pattern: Activities never touch the database directly — all SQL is centralized in StudyRepository.java
• Foreign keys with ON DELETE CASCADE: deleting a deck automatically removes its cards and review logs
• Custom chart view: no MPAndroidChart or similar dependency, keeping the APK small

Each card stores SRS state (easeFactor, intervalDays, repetitions, dueDate). When the user grades a card:

The interval grows exponentially for correctly remembered cards (1 day → 6 days → ~15 days → ~37 days...), so well-known cards appear rarely while forgotten ones come back quickly.

• Android Studio Hedgehog (2023.1.1) or newer
• JDK 17
• Android SDK 34

1. Clone the repository:

   git clone https://github.com/giovergos/study-buddy.git

2. Open the project in Android Studio (File → Open → select the StudyBuddy folder)
3. Wait for Gradle sync to complete
4. Build APK: Build → Generate App Bundles or APKs → Generate APKs
5. The APK will be at app/build/outputs/apk/debug/app-debug.apk

Three tables with proper foreign key relationships:

decks       (_id, name, description, created_at)
cards       (_id, deck_id, front, back, ease_factor, interval_days,
             repetitions, due_date, created_at)
review_logs (_id, card_id, quality, reviewed_at)

• Language: Java 8
• UI: AndroidX AppCompat, Material Components 1.11
• Persistence: SQLite via SQLiteOpenHelper
• Architecture: Repository pattern, no external frameworks
• Min API: 24 (Android 7.0)

MIT License — feel free to use this code for learning or your own projects.

Built as a university assignment to demonstrate Android development fundamentals: multiple Activities, persistent storage, Material Design, clean code practices, and a touch of algorithmic substance via the SM-2 implementation.