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https://github.com/chriseborowski/walletone

A robust Java-based virtual credit card management system featuring constant-time operations, multi-key indexing, and scalable architecture. Utilizes HashMaps for O(1) lookups, implements memory-efficient data structures, and supports multi-user card management. Offers card addition, removal, card/user searches, and card info display.
https://github.com/chriseborowski/walletone

command-line command-line-tool credit-card credit-card-management credit-card-management-system credit-card-manager credit-card-menu-interaction finance-management financial-technology java java-app virtual-credit-card

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A robust Java-based virtual credit card management system featuring constant-time operations, multi-key indexing, and scalable architecture. Utilizes HashMaps for O(1) lookups, implements memory-efficient data structures, and supports multi-user card management. Offers card addition, removal, card/user searches, and card info display.

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# WalletOne: Virtual Credit Card Management System



  WalletOne: Virtual Credit Card Management System



WalletOne is a robust Java-based virtual credit card management system designed for efficient handling of card information, user data, and related operations, all in the command-line interface (CLI). For a detailed description and overview of WalletOne's main functionalities, see this blog post: [Introducing WalletOne: An Interactive Java Backend App Featuring a Virtual Credit Card Management System](https://chriseborowski.notion.site/Introducing-WalletOne-An-Interactive-Java-Backend-App-Featuring-a-Virtual-Credit-Card-Management-Sy-ae31693fde4249f28a142ddda560f637).



## Key Features



- [x] Add and remove credit cards with unique card numbers

- [x] Manage multiple users per card

- [x] Search functionality by zip code and user name

- [x] Display detailed card information

- [x] Constant-time card lookup using hash-based data structures

- [x] Efficient user management with multi-key indexing



## Technical Highlights



- **Constant-time Card Lookup**: Utilizes HashMap for O(1) card retrieval by card number

- **Multi-key Indexing**: Implements separate HashMaps for zip code and name-based user lookups

- **Memory-efficient User Storage**: Uses a shared User object across different indexes

- **HashMap-based Card Storage**: 

  The `CardManager` class uses a `HashMap` (cardHashMap) for O(1) card retrieval by card number.

- **Scalable Architecture**: Designed to handle a large number of cards and users efficiently



## Installation



1. Ensure you have Java Development Kit (JDK) 8 or higher installed on your system.

2. Clone the repository:

   

`git clone https://github.com/chriseborowski/walletone.git`



3. Navigate to the project directory:

   

`cd walletone`



4. Compile the Java files:



`javac -d bin src/walletone/*.java`



## Usage



1. Run the main application:



`java -cp bin walletone.Main`



2. Follow the on-screen prompts to interact with the system.



## Class Structure



- `Card`: Represents a credit card with associated users

- `User`: Represents a card user with name and zip code

- `CardManager`: Core class managing all card operations and user lookups

- `Main`: Entry point of the application (not provided in the context, but assumed to exist)



## Key Methods



- `addNewCard`: Adds a new card to the system

- `removeCard`: Removes a card and updates all related data structures

- `addUserToCard`: Adds a new user to an existing card

- `searchByZip`: Retrieves users by zip code

- `searchByName`: Retrieves users by name

- `showAllCards`: Displays information for all cards in the system



## Performance Considerations



- Card lookup: O(1) time complexity

- User lookup by zip code or name: O(1) average case, O(n) worst case where n is the number of users with the same zip code or name

- Adding/Removing cards: O(1) time complexity

- Adding users to a card: O(1) amortized time complexity



## Future Enhancements



- Implement data persistence (database integration)

- Add user authentication and authorization

- Develop a graphical user interface (GUI)

- Implement card transaction tracking and analysis



## Contributing



Contributions are welcome! Please feel free to submit a pull request.



## License



This project is licensed under the MIT License - see the [LICENSE.md](LICENSE.md) file for details.