Calendar Application

Event management system with MVC architecture, design patterns, and dual CLI/GUI interfaces

Key Features: MVC Architecture | Strategy Pattern | SOLID Principles | CLI + GUI Interfaces

Overview

A calendar management system supporting multiple calendars with independent timezones, recurring events, and both command-line and graphical user interfaces. Demonstrates clean software architecture with proper separation of concerns.

Core Capabilities:

• ✅ Multiple calendars with independent timezone support
• ✅ Recurring events with flexible weekly patterns
• ✅ Dual interfaces - CLI (interactive & file-based) and GUI (Swing)
• ✅ Design patterns: Strategy, Command, Factory, Builder
• ✅ SOLID principles throughout codebase

Architecture

MVC with Service Layer

View Layer (CLI/GUI) → Presentation only, no business logic
         ↓
Controller → Coordinates user actions, calls model
         ↓
DTO/Service Layer → Transforms input into structured data
         ↓
Model Layer:
  - CalendarModel (Business coordinator)
  - Strategy Layer (Operation algorithms)
  - Domain Entities (Calendar, Event - immutable)
  - Storage (CalendarCollection interface)

Design Patterns:

• Strategy Pattern: 15+ strategies for different operations (create, edit, query, copy, export)
• Builder Pattern: Immutable domain objects with validated construction
• Command Pattern: CLI commands encapsulated as DTOs
• Factory Pattern: Strategy selection and instantiation

SOLID Principles:

• Single Responsibility: Each strategy handles one operation type
• Open/Closed: New operations added via new strategies without modifying existing code
• Interface Segregation: Specific interfaces for each operation
• Dependency Inversion: Controllers depend on abstractions, not implementations

Key Features

Calendar Management

• Create multiple calendars with custom timezones
• Edit calendar names and timezones
• Switch between calendars seamlessly
• Timezone conversion with automatic event time adjustment

Event Creation & Editing

• Single events: One-time timed or all-day events
• Recurring events: Weekly patterns (M/T/W/R/F/S/U), repeat N times or until date
• Edit scopes: Single occurrence, this and future, or entire series
• Multi-property editing (GUI only) - Change subject, time, location, description together
• Bulk edit: Search and modify multiple matching events

Advanced Operations

• Copy events between calendars with timezone conversion
• Weekday pattern preservation in bulk copy
• Export to Google Calendar CSV or iCalendar (.ics)
• Availability checking at specific times
• Duplicate prevention

Application Interfaces

GUI Mode

Swing-based interface with calendar grid, navigation, and event management

Features:

• Calendar dropdown selector
• Month navigation (Previous/Today/Next buttons)
• Date selection grid
• Event list panel for selected date
• Create/Edit buttons for calendars and events
• Search & bulk edit functionality

CLI Mode

$ java -jar calendar-1.0.jar --mode interactive

Welcome to Calendar!
> create calendar --name "Work" --timezone "America/New_York"
New calendar 'Work' created.

> create event "Team Meeting" from 2025-12-01T10:00 to 2025-12-01T11:00 repeats MWF for 10 times
events created now is 10

> print events on 2025-12-01
1 event(s) found:
1. Event{subject='Team Meeting', startDateTime=2025-12-01T10:00...}

How to Use

Build the Application

# Build JAR file using Gradle
./gradlew clean build

# JAR created at: build/libs/calendar-1.0.jar

Running the Application

GUI Mode (Recommended for beginners)

java -jar build/libs/calendar-1.0.jar

Quick Start:

1. Application opens with default calendar
2. Click "Create Calendar" to add your own calendar
3. Select a date on the grid
4. Click "Create Event" to add events
5. Use navigation buttons to browse months
6. Click dates to view events in the side panel

CLI Interactive Mode (For power users)

java -jar build/libs/calendar-1.0.jar --mode interactive

Common Commands:

# Create calendar
create calendar --name "Work" --timezone "America/New_York"

# Set active calendar
use calendar --name "Work"

# Create single event
create event "Meeting" from 2025-12-01T10:00 to 2025-12-01T11:00

# Create recurring event (every Monday/Wednesday/Friday, 10 times)
create event "Standup" from 2025-12-01T09:00 to 2025-12-01T09:15 repeats MWF for 10 times

# Create all-day event
create event "Holiday" on 2025-12-25

# Query events on date
print events on 2025-12-01

# Edit single occurrence
edit event subject "Meeting" from 2025-12-01T10:00 to 2025-12-01T11:00 with "Sprint Planning"

# Export calendar
export cal my_calendar.csv

CLI Headless Mode (For automation)

java -jar build/libs/calendar-1.0.jar --mode headless path/to/commands.txt

Example commands.txt:

create calendar --name "School" --timezone "America/Chicago"
use calendar --name "School"
create event "Class" from 2025-12-01T10:00 to 2025-12-01T11:30 repeats MWF for 15 times
export cal school_calendar.ical

Technical Implementation

Core Design

Immutability:

• All domain objects (Calendar, Event) immutable with final fields
• Modifications create new instances, ensuring data integrity

Timezone Handling:

• Each calendar has independent ZoneId
• Events use ZonedDateTime for proper timezone representation
• Cross-timezone copying automatically adjusts times
• Handles daylight saving time transitions

Recurring Events:

• Separate Event objects sharing common seriesId (UUID)
• Three edit scopes: single, forward, or entire series
• Weekday pattern preservation in bulk operations

Storage:

• CalendarCollection interface abstracts storage
• Current implementation: in-memory HashMap
• Easily replaceable with database or file storage

Tech Stack

Language: Java 11+
UI: Java Swing (GUI), Console I/O (CLI)
Build: Gradle
Date/Time: java.time API (ZonedDateTime)
Patterns: MVC, Strategy, Builder, Command, Factory

⭐ Demonstrates clean architecture, design patterns, and software engineering best practices