Where the code is

Verified against Minecraft 26.3 · Maps · The jar as a treemap of packages: area is lines of decompiled source, colour is which jar ships the package, hatching is the packages Part I’s what this book skips tours.

Java Minecraft is 7,301 classes and 741,069 lines of decompiled Java 25, and the first surprise in it is how little of that the client owns alone. Everything a player sees — every screen, the HUD, the whole renderer, the entity models, both GPU back-ends, the sound engine, Realms — is the orange near-third of this picture. The blue seven tenths ship in both jars, and the biggest inner box, world/level, is a fifth of the game by itself: blocks, block states, chunks, lighting and world generation, all of it code the dedicated server runs with no window attached.

Two jars, one tree

The client jar is a strict superset of the server jar, and the split is clean: the 2,264 client-only classes live in exactly five packages — net/minecraft/client (1,891 classes), com/mojang/renderpearl (146), com/mojang/realmsclient (137), com/mojang/blaze3d (86) and net/minecraft/realms (4). Every other package in the table below ships in both jars, class for class; no sub-package at this depth is mixed. The client-only side is 220,818 lines, 29.8% of the total, which is the “just under a third” the introduction quotes.

The consequence for reading this book: when a page says a class is client-only it is saying which package the class lives in, and every package Parts IV and V own ships in both jars. The oracle for which side a class is on is server-classes.txt.

What the big boxes are

world — 42%. world/level (151,146 lines, 1,418 classes) is Parts IV, V and XII: chunks, block states, lighting and, under world/level/levelgen, most of world generation — world/level/biome is its sibling rather than part of it. world/entity (110,760 lines, 727 classes) is Parts VI and VIII: the entity hierarchy, its AI and the player. world/item and world/inventory (37,813 lines between them) are Part VII.

client — 24%. client/gui (59,594 lines) is the screens and the HUD, Part X; client/renderer and client/model (63,361 lines together) are the frame, section meshing and the entity models, Part XI; client/multiplayer (11,303) holds ClientPacketListener and ClientLevel, the client’s copy of the world. The 41 classes directly in net/minecraft/client — Minecraft, Options, KeyMapping, MouseHandler — are 10,821 lines on their own. (That 41 is the itself only count defined below; the 1,891 above is the package with every sub-package under it.)

util — 7%, two thirds of it skipped. util/datafix, util/filefix and util/profiling are 34,866 of the package’s 54,700 lines and are all outside this book; the hatched boxes are those three, and much the largest of them is the save-migration history. What is left is the toolbox every part uses — Mth, RandomSource, Util — and the parsing and debug packages.

server — 7%. server/commands (13,357) is Part XIII’s command implementations; server/level is 42 classes and 12,166 lines — 290 lines a class, nearly three times the map’s average, in a package small enough to list (ServerLevel, ChunkMap, ServerPlayer), Parts III and IV; server/network is the serverbound packet handlers, Part IX; server/packs is the pack system, Part II; server/jsonrpc, the management server, is skipped.

renderpearl and blaze3d — 4%. The GPU abstraction, com/mojang/renderpearl, has two back-ends behind GpuDevice, and the Vulkan one (renderpearl/backend/vulkan, 7,387 lines) is larger than the OpenGL one (renderpearl/backend/opengl, 5,815); com/mojang/blaze3d keeps the window, the frame graph, the vertex formats and RenderSystem.

network — 3%, in 416 classes. network/protocol is 298 classes in 12,872 lines: the packet catalogue is many tiny classes, one per packet. network/chat (4,799) is Component and chat signing.

Below 3% the other boxes include Part II’s foundations — net/minecraft/core, net/minecraft/nbt, net/minecraft/tags, net/minecraft/resources — and Part XIII’s net/minecraft/commands (the command source, the argument types and the execution engine) and net/minecraft/advancements, plus com/mojang/realmsclient and the skipped net/minecraft/data. That last one is the program that writes the vanilla data pack — and it is not build-time only: the dedicated server ships all 174 classes, and Blocks and MinecraftServer both read data/worldgen constants at run time (what this book skips sorts every such reader into three kinds).

Where each part lives

The parts follow the tree, but not one box each. This table is the map from the book’s order to the jar’s, and it is the one table on this page that is a decision rather than a measurement: the packages are assigned by hand, in the tool that draws the atlas, and the counts follow. A package under net/minecraft is written without that prefix; itself only means the files directly in the package and not its sub-packages; a package two parts share is counted in both and a file in no part’s packages in none, so the total row is not the jar’s. A landing page that states its part’s size quotes its own row of this table, and the hatched packages and player reporting are left out of every row.

The table

Depth three is the outer boxes of the treemap; depth four is the inner ones. client-only counts the classes not in server-classes.txt.

Rules: names, never code · how the system works, not how the code reads · newest version only · every backticked name passes tools/verify_names.py.