Isabel Barroso AgudoI build desktop and backend software with Java and C++.

Problem

A restaurant that delivers has to keep track of the menu, the open orders and which courier has each one, all at once. Customers want to order without installing another app.

Solution

The operator works in a JavaFX application with the menu, the orders and delivery by postcode zones. Customers sign up and order through a Telegram bot, which listens on its own thread so the interface never blocks. Addresses are validated with the Mapbox geocoding API and data is stored in MySQL 8 through JPA/Hibernate.

What I learned

To design an application before coding it: starting from UML diagrams and an entity-relationship model to reach the MySQL schema. Mapping it with JPA/Hibernate showed me how a layered architecture is organised and how much it matters to model the life cycle of an order properly from the start. I also learned to document a project so that other people can understand it.

• 10 JPA entities and an order with 6 states. Transitions are validated in a single place in the service layer and every change is written to a history table.
• Couriers are assigned by hand or automatically from the free couriers in the order’s zone.
• Operator passwords hashed with BCrypt.
• 38 JUnit 5 tests, including integration tests on H2.
• Written report with use cases, class diagram, entity-relationship model, state and deployment diagrams.

Technologies

• Java 21
• JavaFX
• Hibernate/JPA
• MySQL 8
• Docker
• JUnit 5
• Telegram API
• Mapbox

• Code on GitHub ↗
• Project report (PDF, in Spanish) ↗
• Data model ↗

Problem

To help someone with their computer you need to see their screen. I wanted to do it without typing addresses by hand and without anything being shared behind the other person’s back.

Solution

The client looks for machines with a UDP broadcast and lists the ones that answer. Choosing one opens a TCP connection. The host sees a dialog to allow or reject it; if accepted, it sends its screen size and then ten JPEG captures per second, each preceded by its size in bytes.

What I learned

To work with low-level networking in Java: discovering machines over UDP, connecting over TCP with sockets and designing my own protocol to send images. I had to use threads to listen for connections without blocking the application and to handle closing the connection from both sides. I also learned that privacy belongs in the design: nothing is shared without permission and there is always a visible indicator.

• Explicit permission from the host before anything is shared. If rejected, the socket is closed.
• A red bar stays visible on the host while the screen is being shared.
• The host can cut the connection at any time and the client is told it has ended.
• Current limit: it only works inside the same local network.

Technologies

• Java
• TCP sockets
• UDP
• Threads

• Code on GitHub ↗

The commission

The CyberAcademy website belongs to someone else, who asked me to turn it into a desktop application in Java.

How it works

Learners earn experience and achievements and have a level for each skill. That level adjusts to how they solve each exercise: how long they take and whether they ask for hints. Solving bubble sort with a hint raises the level less, or even lowers it.

What I learned

To work on a project I had not created: understanding how it works before touching it, and moving an interface and logic designed for the web to a desktop environment while respecting what the client needed.

Technologies

• Java