Price Stock Exchange

A command-line stock exchange simulation built for Object-Oriented Software Development. It models orders, quotes, product books, users, and live “current market” updates.

What I Learned & Implemented

Object-Oriented Fundamentals

• Encapsulation: Domain objects keep state private; updates go through validated methods. Shared read-only views use DTOs to avoid leaking internals.
• Immutability: Price is an immutable value type (stored as cents int to avoid floating-point drift) and implements Comparable.
• Interfaces & Polymorphism: Tradable abstracts both orders and quote sides, letting the book match them uniformly.

Design Patterns (with intent, not just names)

• Factory: PriceFactory normalizes creation (parsing "$1,234.56" → cents) and centralizes validation.
• Flyweight: PriceFactory returns one shared instance per price value, reducing memory churn across the book.
• Singleton: UserManager and ProductManager expose one source of truth for users and product books.
• Façade: Those managers provide a simple API while hiding coordination logic (routing tradables to the right book, user updates, etc.).
• Observer (Publish/Subscribe): CurrentMarketPublisher notifies subscribed users when top-of-book changes; User implements CurrentMarketObserver.

Data Structures & Algorithms

• Order book: TreeMap<Price, List<Tradable>> for each side

  • BUY: descending by price; SELL: ascending.
  • Efficient top-of-book lookups and price-level aggregation.

• Lookups: HashMap for users, products, and user-specific quote/order tracking.

• Matching logic:

  • ProductBook.tryTrade() computes tradable volume across sides.
  • ProductBookSide.tradeOut(price, vol) proportionally fills across price-level entries, updates filled/remaining/cancelled, and emits fills.

Error Handling & Validation

• Purpose-built exceptions (e.g., InvalidPriceException, data-validation errors).
• Strict input rules for user IDs, symbols, volumes, and price formats.

Testing Hooks

• A provided Main script exercises: adding orders/quotes, cancelling, trading, and current-market publications. Output is deterministic for quick verification.

How to Run

Prereqs

• JDK 17+ installed (java -version to confirm)

Clone

git clone <your-repo-url>
cd <repository-folder-name>

Compile (Adjust the main class path if your Main has a package.)

javac -d out --source-path src src/Main.java

Run

java -cp out Main

You’ll see console output showing adds/cancels, fills, and current-market snapshots (e.g., WMT $70.70x35 - $70.75x40 [$0.05]).