digital-wallet-system.md

Designing a Digital Wallet System

In this article, we will explore the object-oriented design and implementation of a Digital Wallet System using Java.

This system facilitates online transactions, enabling users to store money digitally and make secure payments.

System Requirements

The Digital Wallet System should:

1. User Account Management: Manage user account creation and maintenance.
2. Wallet Management: Allow users to add, withdraw, and check balances.
3. Transaction Processing: Handle transactions and maintain a history.
4. Security and Authentication: Ensure secure access and transaction integrity.

Core Use Cases

1. Creating and Managing User Accounts
2. Adding and Withdrawing Funds
3. Making and Receiving Payments
4. Viewing Transaction History

Key Classes:

• DigitalWalletSystem: Manages the system.
• User: Represents a user.
• Wallet: Manages a user's wallet.
• Transaction: Represents a transaction.

Java Implementation

User Class

Manages user account information.

public class User {
    private String userId;
    private String name;
    private Wallet wallet;

    public User(String userId, String name) {
        this.userId = userId;
        this.name = name;
        this.wallet = new Wallet(this);
    }

    // Getters and setters...
}

Wallet Class

Represents a user's digital wallet.

import java.util.ArrayList;
import java.util.List;

public class Wallet {
    private User user;
    private double balance;
    private List<Transaction> transactionHistory;

    public Wallet(User user) {
        this.user = user;
        this.balance = 0.0;
        this.transactionHistory = new ArrayList<>();
    }

    public boolean addFunds(double amount) {
        if (amount <= 0) {
            return false;
        }
        balance += amount;
        transactionHistory.add(new Transaction("Deposit", amount, balance));
        return true;
    }

    public boolean withdrawFunds(double amount) {
        if (amount > balance) {
            return false;
        }
        balance -= amount;
        transactionHistory.add(new Transaction("Withdrawal", amount, balance));
        return true;
    }

    // Getters and setters...
}

Transaction Class

Represents a financial transaction.

import java.util.Date;

public class Transaction {
    private String type;
    private double amount;
    private Date date;
    private double postTransactionBalance;

    public Transaction(String type, double amount, double postTransactionBalance) {
        this.type = type;
        this.amount = amount;
        this.date = new Date();
        this.postTransactionBalance = postTransactionBalance;
    }

    // Getters and setters...
}

DigitalWalletSystem Class

Manages the digital wallet system operations.

import java.util.ArrayList;
import java.util.List;

public class DigitalWalletSystem {
    private List<User> users;

    public DigitalWalletSystem() {
        this.users = new ArrayList<>();
    }

    public void addUser(User user) {
        users.add(user);
    }

    public boolean transferFunds(String senderUserId, String receiverUserId, double amount) {
        User sender = users.get(senderUserId);
        User receiver = users.get(receiverUserId);

        if (sender != null && receiver != null) {
            Wallet senderWallet = sender.getWallet();
            Wallet receiverWallet = receiver.getWallet();

            if (senderWallet.deductFunds(amount)) {
                receiverWallet.addFunds(amount);
                return true;
            }
        }
        return false;
    }
    
    // Other necessary methods...
}