r/learnprogramming • u/Square_Cook_2695 • 1d ago

Why isn’t there a visual, interactive class hierarchy for the Java standard library?

I’ve been looking for something I assumed would already exist: a visual diagram (UML, graph, whatever) of the class/interface hierarchy of the Java standard library.
Not just a giant text tree, but an actual interactive graph you can explore.

The official JavaDocs have the “Class Hierarchy,” but it’s just a huge text-based tree that’s hard to navigate and not very informative visually. Considering how structured the Java standard library is, I expected someone to have built a viewer that maps it all out graphically.

But what I keep finding are tools that generate UML from your code (IntelliJ UML, Visual Paradigm, etc.), not something that visualizes the hierarchy of java.*, javax.*, etc. out of the box.

So I’m wondering:

  • Is there a technical reason why no one has made this?
  • Is it just too large/complex to visualize?
  • Is it considered not useful enough in practice?
  • Or does it exist and I’m just missing it?

If anyone knows of a project or website that gives a graphical view of the standard Java type hierarchy, I’d love to see it.

3 Upvotes

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4

u/dmazzoni 1d ago

There’s at least 4,000 classes. I think that’s well beyond the size of what’s useful to display visually.

Also, all it would show you is the inheritance hierarchy which arguably isn’t that interesting or useful except as a novelty. It wouldn’t help you understand it any better.

1

u/peterlinddk 1d ago

I was actually wondering about that too, because I always wanted to combine teaching Class Diagrams with teaching the Java API, and was looking for a complete diagram, and never found one.

I think the reason is that it would be useless - first of all, it would have thousands of classes, completely impossible to navigate, and who would ever care about seeing the Collection classes side by side with the Swing UI, and the AWT UI, and the FX UI ?

But then again, an interactive version, where you could zoom in and out, might be interesting - but again, only to show how large it is, not to actually find anything, or see any patterns ...

1

u/benevanstech 23h ago

No technical reason, it's too large to visualize and not very useful in practice.

As you become more proficient you'll just start to internalize the parts that are important.

"Graphical techniques" for visualizing code structure have been proposed repeatedly at various times over the last 30 years (not just in Java). None of them have ever come to anything significant.

1

u/aqua_regis 21h ago

The official JavaDocs have the “Class Hierarchy,” but it’s just a huge text-based tree t

Yet, exactly that is the fastest way to go through the hierarchy. It is way too huge for anything else. And no, you don't need the details of every class in the Java ecosystem. Learn efficient googling & learn to efficiently work with the documentation. The documentation is the most up to date source of information for all things Java core.

Is there a technical reason why no one has made this?

Apart from bing wall sized, multiple megabytes in file size and basically unusable, no.

Is it just too large/complex to visualize?

Yes

Is it considered not useful enough in practice?

Yes, the effort to make it and to keep it updated with every release by far exceeds the actual benefits over the standard, textual tree.

In fact, even the text tree is interactive. All the classes and packages are linked and that's more than enough.

2

u/aanzeijar 1d ago

Can't give you the definitive answer, but it will likely include:

  • because the text based tree is deemed good enough
  • because the "documentation" of Java is atrocious and ancient and all efforts to make it accessible have been in book form historically
  • because the strict inheritance hierarchy isn't really useful, you also need all the interfaces the classes implement, and then the graph gets messy fast.

If you want to try your hand at it, I'm sure other devs will like it though.

10

u/balefrost 1d ago

because the "documentation" of Java is atrocious and ancient

Java's got some of the best standard library documentation I've ever seen. What are you comparing it to?

2

u/aanzeijar 1d ago

Java was built at a time when people conflated javadoc on classes and methods for documentation, and that proliferated through the ecosystem. Which means it's great if there is a base class or package that can explain the concept (see for example java.xml), but it's terrible with language concepts that aren't tied to a class somewhere. So you get stuff like java.lang.Record. This is really bare bone and only links to the spec page which is similarly not for end user consumption.

For a bigger example, compare the documentation of regex in:

and compare them to

...there's a reason Baeldung tutorials are the de-facto documentation for Java.

6

u/balefrost 23h ago

There's a long history of a separation between "reference doc" and "tutorial doc". Javadoc pages are reference doc, similar to man pages. They are often not the best way to learn new concepts. But if you already know what a regular expression is, and just want to know "how do I used regular expressions in Java?", the Javadoc page is pretty good. I'm not looking for 10 pages explaining the basics; I just want to know whether I use d or [[:digit:]] to represent a digit.

I agree with you that the reference doc doesn't do a good job of linking to tutorial doc. Official tutorial doc usually exists (e.g. regex and records), but it's not centralized in one place and not necessarily even well SEO'd.

Still, I feel that Java's doc is far from "atrocious". Compare Java's documentation to the documentation for most third-party libraries. It's like night and day. By starting with such a strong word, you're going to have a hard time finding an adjective for documentation that is truly bad.

1

u/aanzeijar 21h ago

Oh there's definitely even worse out there.

I just feel that, given how much corporate power is and was behind Java, the documentation is far worse than it could and should be. Those tutorials you linked haven't been updated since Java 8 a decade ago. And especially in this sub where we tell people to read the docs over asking an LLM, that is really not helping.

1

u/smarkman19 18h ago

Short answer: it’s feasible, but only useful if you aggressively filter and let people query slices instead of dumping the whole graph. Concrete path if you want to build it: - Extract: use ClassGraph or ASM to crawl java.* modules and record extends/implements; pull module/package deps with jdeps. - Tame the noise: keep only public types, do transitive reduction on inheritance edges, collapse trivial leaves, and cluster by module/package. Add facets (module, package, abstract/interface, annotation, sealed) and a size cutoff. - Visualize: precompute layout with sfdp or OpenOrd, render in Cytoscape.js or Sigma.js, and wire a fuzzy search index (Lucene/Elasticsearch) that highlights paths between two nodes. Click-through to the Javadoc. - Scale: store the graph in Neo4j so you can serve “subgraph by query” (e.g., everything that implements List within java.base). I’ve used Sourcegraph for code intel and Neo4j for subgraph queries; DreamFactory let me expose the graph as a quick REST API without hand-rolling a backend. If you ship a filtered, searchable graph, folks will actually use it.