Features Required:

User Registration and Authentication: Users should be able to create accounts, log in, and authenticate themselves to access the cryptocurrency exchange platform.
Wallet Management: Users should be able to create and manage cryptocurrency wallets to hold their digital assets.
Trading Pairs and Order Book: The platform should support various trading pairs and maintain an order book to match buy and sell orders.
Order Placement and Execution: Users should be able to place buy or sell orders for cryptocurrencies, and the platform should execute trades based on market conditions.
Balance and Portfolio Tracking: Users should be able to track their account balances, transaction history, and portfolio performance.
Deposit and Withdrawal: Users should be able to deposit or withdraw cryptocurrencies to or from their wallets.
Market Data and Charts: The platform should provide real-time market data, price charts, and other relevant information for users to make informed trading decisions.
Security Measures: The platform should implement security measures, such as two-factor authentication, encryption, and robust account protection mechanisms.

Design Patterns Involved or Used:

Model-View-Controller (MVC) Pattern: The MVC pattern can be used to separate the application into three components: the model (data and business logic), the view (user interface), and the controller (handles user interactions and manages the flow of data).
Singleton Pattern: The Singleton pattern can be used to ensure that only one instance of certain classes, such as the user authentication manager or the order book manager, is created and shared across the system.
Factory Pattern: The Factory pattern can be used to create different types of objects, such as users, wallets, or orders, based on user requests.
Observer Pattern: The Observer pattern can be used to notify users about changes in account balances, transaction history, or trade execution.
Decorator Pattern: The Decorator pattern can be used to add additional functionality or features, such as transaction fees, account verification, or advanced trading options, to the core classes in the system.
Proxy Pattern: The Proxy pattern can be used to handle communication between clients and the actual cryptocurrency exchange, providing a level of indirection and encapsulation for network operations.

Code: Classes Detailed Implementation Based on Patterns Mentioned Above

// User class
class User {
    private String userId;
    private String username;
    private String password;
    // Other attributes and methods

    public User(String userId, String username, String password) {
        this.userId = userId;
        this.username = username;
        this.password = password;
    }

    // Getters and setters
}

// Wallet class
class Wallet {
    private String walletId;
    private User user;
    private Map<String, Double> balances;
    // Other attributes and methods

    public Wallet(String walletId, User user) {
        this.walletId = walletId;
        this.user = user;
        this.balances = new HashMap<>();
    }

    public void deposit(String currency, double amount) {
        // Perform logic to deposit funds into the wallet
        balances.put(currency, balances.getOrDefault(currency, 0.0) + amount);
    }

    public void withdraw(String currency, double amount) {
        // Perform logic to withdraw funds from the wallet
        double currentBalance = balances.getOrDefault(currency, 0.0);
        if (currentBalance < amount) {
            throw new IllegalArgumentException("Insufficient balance");
        }
        balances.put(currency, currentBalance - amount);
    }

    // Other wallet operations
}

// Order class
class Order {
    private String orderId;
    private User user;
    private String tradingPair;
    private String type;
    private double price;
    private double quantity;
    // Other attributes and methods

    public Order(String orderId, User user, String tradingPair, String type, double price, double quantity) {
        this.orderId = orderId;
        this.user = user;
        this.tradingPair = tradingPair;
        this.type = type;
        this.price = price;
        this.quantity = quantity;
    }

    // Getters and setters
}

// Observer interface
interface BalanceObserver {
    void update(String walletId);
}

// BalanceTracker class
class BalanceTracker implements BalanceObserver {
    private User user;

    public BalanceTracker(User user) {
        this.user = user;
    }

    @Override
    public void update(String walletId) {
        // Update account balances for the user
        System.out.println("Account balances updated for user " + user.getUsername() + ", wallet: " + walletId);
    }
}

// Main Class
public class CryptoExchangePlatform {
    public static void main(String[] args) {
        // Create users
        User user1 = new User("user1", "John", "password1");
        User user2 = new User("user2", "Alice", "password2");

        // Create wallets
        Wallet wallet1 = new Wallet("wallet1", user1);
        Wallet wallet2 = new Wallet("wallet2", user2);

        // Create balance trackers
        BalanceTracker balanceTracker1 = new BalanceTracker(user1);
        BalanceTracker balanceTracker2 = new BalanceTracker(user2);

        // Subscribe balance trackers to wallets
        wallet1.subscribeObserver(balanceTracker1);
        wallet2.subscribeObserver(balanceTracker2);

        // Deposit funds into wallet1
        wallet1.deposit("BTC", 1.5);

        // Withdraw funds from wallet2
        wallet2.withdraw("ETH", 2.0);
    }
}

In this code example, the User class represents a user of the cryptocurrency exchange platform, the Wallet class represents a wallet to hold digital assets, the Order class represents a buy or sell order for cryptocurrencies, and the BalanceTracker class implements the BalanceObserver interface to track and update account balances for users.

The code demonstrates the usage of classes based on the mentioned patterns, such as the Observer pattern for tracking and updating account balances, the Singleton pattern (not explicitly shown in the code) for creating a single instance of the user authentication manager or the order book manager, the Factory pattern for creating different objects based on user requests, the Decorator pattern (not explicitly shown in the code) for adding transaction fees or account verification to the core classes, and the Proxy pattern (not explicitly shown in the code) for handling communication between clients and the actual cryptocurrency exchange.

Please note that this is a simplified example, and a complete implementation of a cryptocurrency exchange platform involves more complex components, such as market data feeds, order matching algorithms, trade execution, order history tracking, KYC procedures, multi-factor authentication, and integration with external cryptocurrency networks and services.

Design (LLD) a cryptocurrency exchange platform - Machine Coding