Advice on developing my first Java POS application for a small grocery store

[u/Yrpx]

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Hi everyone,

I'm a web and mobile development student. I have some programming knowledge, but this is my first time developing a complete application from start to finish.

I've received my first request to build a POS system for a small grocery store, and I'd like to do a good job while also learning from the experience.

The store has only one cashier, so the application should be simple and practical.

The main requirements are:

Register products by scanning their barcodes and entering their names, prices, and quantities.

Scan products during checkout and automatically display their names and prices.

Calculate the total and save each sale.

Automatically update stock quantities after each sale.

Review previous sales and check current inventory.

I'd prefer a desktop application that works offline on a single computer.

I'd like to use Java and a database, including SQL if needed, since these are among the technologies I've studied and want to apply in a real project.

I'd appreciate your advice on the following:

Is there an existing free and open-source Java POS application that would be suitable for a small grocery store? I'd like to study its code, understand how it works, and modify it to meet the requirements.

If such a project exists, which ones would you recommend, preferably projects that are reasonably well-organized, functional, and easy to modify?

If modifying an existing project isn't a good option, would building the application from scratch be better?

If I build it from scratch, what technologies would you recommend for the user interface and database?

Could you suggest a step-by-step development roadmap suitable for someone who knows programming basics but hasn't built a complete application before?

Since this is my first client project, I want to choose a sensible approach rather than waste time on an unsuitable codebase. My goal is to deliver a working application while understanding the code and learning how to develop a complete software project.

I'd appreciate any practical advice, project recommendations, or lessons from your experience. Thank you!

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[u/Dashing_McHandsome]

You should have someone more senior with you on this project. I don't want to discourage you, but there's a lot to this that you may not have seen before. You may be very capable, I really have no idea. But no amount of talent can replace years of experience and knowing where you are going to get bitten on this type of a project.

Edit: clarifying my statement

[u/Yrpx → u/Dashing_McHandsome]

I understand and agree with your point... There are many things I still need to learn about this kind of project, but this is an opportunity with my first potential client, and I don't want to miss it just because I'm still learning. I see it as a chance to gain real-world experience and improve my skills. Any advice, guidance, or a roadmap for structuring and building the project would be greatly appreciated, especially if it helps me understand what to focus on and avoid common mistakes.

[u/Far-Bullfrog161]

Congrats on the first client, and good call on wanting a sensible approach. For a one-cashier offline shop I'd build from scratch rather than modify a big existing POS, because those tend to carry lots of features you don't need and are harder to understand than a small app. Keep the stack boring: JavaFX or Swing for the UI, and SQLite or H2 as an embedded database so there is no server to install. Split the code into layers (UI, service logic, database access) so the UI isn't full of SQL. Model a few tables first: products (with barcode as a unique column), sales, and sale items. Do the stock update and the sale insert in one database transaction so they can't get out of sync. Most barcode scanners just act like a keyboard that types the code and presses Enter, so you can test without hardware. Build it in small steps: add products, then the checkout screen, then stock updates, then sales history. Also set up automatic backups of the database file, since losing a shop's sales data is the thing that would hurt most.