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Essential Minecraft Concepts

This section was designed as a 10,000m overview for beginners by beginners, covering essential concepts and definitions needed as background knowledge before you start your first mod. Some concepts relate to elements visible in game, others to used files or classes that are frequently used while modding.

Concept	Description

Item	Something you can hold in your hand, drop to the ground, place in inventory or store it in a container. It may be a tool or a block held in the hand before placing it.
Block	The key component for anything you build in minecraft and has been placed in the world. A lot of blocks are cubes, but most things you place in the world are implemented as blocks, like a furnace. Some blocks don't even look much like a cube, like buttons, fences and doors, and yet they are still treated as blocks. It is important to note that a Block should be thought in code as the definition for a type of block, not the actual single block you see in game.
Blockstate	Blockstates (often seen in code under the name 'state') a specific instance of a block placed in a specific position in the world. This is what you normally think as a block while playing.
Block Item	The item form of a block, so that you can hold them in your hand, stack them and store them.
Living Entity	Something alive and moving in the world, like players and mobs.
Entity	An internal structure to hold state data. For example, BlockEntity for blocks or ItemEntity for items, and of course LivingEntities. Some other things are occasionally also implemented as entities, like projectiles, frames and paintings. For example, the information about a torch placed at a given position in the world being on or off is stored in the torch's entity.
Model	The model is a set of descriptive data used to represent the structure of a block, item, living entity, etc. For example, an iron block or furnace would contain information to describe the shape and size of each of its faces, as well as information about where to find the texture(image) that is used to give a particular surface its unique look. Models are usually described in JSON files but can also be setup via Java code.
Texture	These are the graphic images used to give surfaces their unique look. They are usually implemented as 16×16 pixel .PNG files.
Renderer	While most mods make use blockstates and model JSON files plus .PNG textures to provide the full representation of blocks, items and entities and rely on the default rendering mechanism to show them in the world as you'd expect, there are situations when you will need more complex behaviors. In those cases you will need to create a custom renderer to achieve the desired result.
NBT	NBT methods are what you use in your Entity class to make sure that your block's data gets stored and loaded from the world's save. Sounds complicated but it is a simple matter of overriding a couple methods and putting a couple lines of code there. This is described well in the section “Adding a BlockEntity”.
Threads	Minecraft is designed in two separate pieces, a client and server piece. When you play on a server the division is clear, but the server piece still exists when you play on your own computer. These pieces are implemented as threads and you need be very aware of them while coding. You will often see a given overridden method being called by both the client and server threads, and to distinguish to which thread you are responding to you will need to test for it. The easiest and most common way is to check with the boolean method world.isClient().
Data Sync	Although you can store block data on its entity, such entity data does not travel automatically between the server and client threads. You need to enable it yourself with a couple lines of code, again following the description in “Adding a BlockEntity”.

This is an early version of the Essential Minecraft Concepts page. There are certainly many concepts that still need to be added. Beginners, if you come across a concept that was not described and that stumped you during your learning, please add it to this page. Experts, please correct any errors you find, keeping the descriptions simple enough so that people that know nothing about Minecraft or Fabric modding will still be able to understand them.