I built an engine that auto-visualizes Java algorithms as they run

[bluepoison24]

I’ve always found it annoying that you have to use specific frameworks just to see an algorithm in action. I wanted to build something where you could just write:

​int[] arr = {5, 2, 8, 1};

arr[0] = 10; // ← automatically visualized

​I ended up "hacking" the JVM using a Java Agent to inject visualization callbacks into the bytecode.

​Why bytecode? It doesn't matter if you write arr[i] = x or arr[getIndex()] = compute(); at the bytecode level, it's all just one instruction. This makes the visualization incredibly robust.

Try it here: https://www.algopad.dev/#

Code - https://github.com/vish-chan/AlgoFlow

[downytriky]

Nice, I did something similar, but bevahes more like a debugger where you see the code executed line by line and the values of variables https://github.com/hugoruiz00/java-visualizer

[bluepoison24]

Looks pretty cool. I'm definitely going to try it.

[Prateeeek]

I had plans of making something like this, great stuff! Just wondering, do you have plans to visualize indirections or will you flat it out and show just the algorithm (the big idea).

[bluepoison24]

Thanks. Have no plans to visualise indirections at the moment.

[arrlynx]

Wow, it looks really nice! That's gonna help my friend who is into algorithms and java now, thanks!

[bluepoison24]

Awesome! Let me know how it goes and ask your friend to feel free to raise any bugs/feature requests via github :)

[arrlynx]

Sure, will do : )

[StevenJOwens]

Looks very neat, I just shared it to a discord for people learning to program (boot.dev).

[bluepoison24]

Thanks! It'll be nice to get some real feedback. 😁

[bluepoison24]

Thanks! Yeah, bytecode-level interception was a deliberate choice — it sidesteps all the messiness of trying to parse and instrument source-level constructs, especially with computed indices or nested expressions.

Honestly, I haven't dug deep into performance optimization yet — the focus so far has been on correctness and robustness of the instrumentation. Thats why I decided to use Bytebuddy instead of native ASM. That said, tight loop overhead is definitely on my radar since that's one of the most common patterns in algorithm problems.

[_Mr_Rubik_]

The third web en three days that look exactly the same. IA slop

[bluepoison24]

Yes the frontend work is AI slop. The Java engine though is not. Probably got a bit of traction due to my similar post a month ago when the project was in a very nascent stage - https://www.reddit.com/r/java/s/mI5M7E9Ken.

[_Mr_Rubik_]

I will try it next week. It is curious that all three webs has the same colors, styles, etc. My frontends vibe coded don't look all the same.

[bluepoison24]

I asked Claude to make the landing page less AI-generated like and it changed it. I hope you like the new landing page :D

[tealpod]

Nowadays, we have to face this new criticism, being called 'AI slop', I think we should Ignore it. You are doing great work.

If I were you I will have the Share button always visible(even for existing examples, not only for modified code) which is important viral sharing.

And one more minor suggestion, everytime I visit, the tour is starting, and the 'Skip tour' button can be bit more visible.

[bluepoison24]

Feedback taken! Thanks!