Finding what depends on a class

What you will build. An answer to a question a 3D city cannot give you: exactly what depends on TypeAdapter, through which member, and on which line of which file.

What you need. The gson.jsonl you produced in Your first code city, and codegraph on your PATH. The model is gson at tag gson-parent-2.14.0.

How long. About 15 minutes.

1. Open the navigator

cd ~/codegraph-tutorial
codegraph navigator gson.jsonl --name gson --serve --host 127.0.0.1

cache: gson.db
model navigator at http://localhost:4178/ — Ctrl-C to stop.

Open http://localhost:4178/.

The cache: gson.db line is codegraph building a SQLite store beside your model so the next command does not re-parse the file. It is a disposable cache; delete it any time. You will query it yourself in Querying the model with SQL.

The header shows what was loaded: 1,855 nodes · 6,236 dependencies.

2. Find the class

Type TypeAdapter in the search box (its placeholder reads Search names and signatures). The tree filters as you type. Search is a plain substring scan over every name and signature, capped at 200 results — and the cap is stated in the UI rather than silently applied, so you always know when you are looking at a slice.

Several things match: TypeAdapter, TypeAdapterFactory, TypeAdapters, ArrayTypeAdapter, and more. Click the plain TypeAdapter — the class in com.google.gson.

3. Read the fan-in

The right-hand panel splits into Incoming and Outgoing, each with its total. For TypeAdapter you get 300 incoming rows and 35 outgoing.

Incoming is sectioned by what kind of dependency each row is, in a fixed vocabulary order:

That breakdown is the point of the navigator. “300 dependencies on TypeAdapter” is a number; “18 of them extend it, 61 call it, 56 hold it in a field” is a fact you can act on.

4. Read one row down to the line

Open the Inheritance section and find ArrayTypeAdapter. The row carries four things:

• the counterpart — ArrayTypeAdapter, clickable, which selects it;
• the member of the selected node the edge lands on, or the member of the counterpart that carries it (prefixed on or via);
• a provenance badge, shown only when the row is not a declared fact;
• the anchor — ArrayTypeAdapter.java:34, with the full repository-relative path on hover.

Line 34 of gson/src/main/java/com/google/gson/internal/bind/ArrayTypeAdapter.java is where that class extends TypeAdapter. No badge, so it is a declared fact: the source literally says so.

Now open Invocations and find the two ArrayTypeAdapter rows:

ArrayTypeAdapter  read(...)    via read    dynamic-candidate   ArrayTypeAdapter.java:75
ArrayTypeAdapter  write(...)   via write   dynamic-candidate   ArrayTypeAdapter.java:108

Those carry a badge. dynamic-candidate means codegraph could not resolve the call to a single target and recorded the candidates instead — a virtual call through an abstract method. It is an inference, it is labelled as one, and it is drawn in a colour no fact uses. Every rendering in codegraph keeps that line; see Facts and inferences.

Under Local variable type the same class appears twice more, this time with a detail naming the variable:

ArrayTypeAdapter  via create   local variable componentTypeAdapter   ArrayTypeAdapter.java:46
ArrayTypeAdapter  via create   local variable arrayAdapter           ArrayTypeAdapter.java:49

A local variable is not something you browse to, so it is not a tree node. It is the reason a dependency exists, so it appears as the detail on the row it explains.

5. Read the colours

Four meanings carry a hue in the navigator and nothing else does:

• cyan — incoming;
• amber — outgoing;
• violet — an inference: any row whose provenance is not declared;
• the selection.

A stub — an external type — is drawn muted and italic rather than in a colour of its own. It is a degraded fact, not a fifth category.

6. Use the other three tabs

The tabs across the top are Navigate, Graph, Cycles and Coupling. Every row in the three report tabs leads back to Navigate, so a finding is always one click from its evidence.

Graph. A force-directed dependency graph (Cytoscape with fcose). Two modes, Modules and Types; node size follows fan-in, and labels appear by zoom tier so the far view stays readable. The selection you made on Navigate is carried over and focused, with incoming cyan and outgoing amber, as everywhere else.

Cycles. The tab carries a count badge — 8 for this model. That is the artifact’s precomputed tangle report, at both levels: one strongly connected component of 8 modules, and seven components at type level, the largest of 30 types. Nothing is recomputed in the browser; it is the same report codegraph analyze --report cycles prints.

Coupling. A sortable table of Name, Fan-in (Ca), Fan-out (Ce) and Instability, switchable between modules and types. Sort by fan-in at type level and the top of the table is Override, String, IOException — external types, because an import of an external type is a real dependency and dropping it silently would understate coupling. Uncheck Show externals in the header to drop them, and gson’s own types surface: JsonReader (fan-in 35, fan-out 28, instability 0.44), then TypeAdapter (33 / 14 / 0.30).

7. Stop the server

Ctrl-C. As with the city, you can write the artifact to a file instead:

codegraph navigator gson.jsonl --name gson --out navigator.json

cache: gson.db
wrote 1041132 bytes to navigator.json (navigator, view all, 1855 nodes, 6236 dependency rows).

That file is the frontend’s only input.

What you have now

• A way to go from “something depends on this” to the file and line that proves it, in three clicks.
• The habit of reading the provenance badge before believing a dependency.
• Four views over one model that cannot disagree with each other, because all four were computed once by the analyzer and only rendered in the browser.

Where to go next

• Replaying a project’s history — the dependency the source cannot show you: what changes together.
• Querying the model with SQL — ask the same questions yourself against model.db.
• The navigator — why there is one classified row per base edge, and how a reference’s role is recovered.