Tutorials

22 chapters covering every feature japes exposes. Each chapter builds on the previous one; by the end you've touched every annotation and service parameter the library ships. The chapters are self-contained — you can skip around — but the basics section should be read roughly in order if you're new to ECS.

Basics

Components, entities, systems, queries, resources, change detection, RemovedComponents, Commands.

Advanced

Events, Local<T>, stages and ordering, multi-threading, @With / @Without, @Where, @Exclusive, run conditions.

Relations

@Relation, @Pair + PairReader, @ForEachPair + @FromTarget, cleanup policies, RemovedRelations, a worked predator/prey example.

Basics

#	Chapter	What you'll learn
1	Components	Why components are records, field rules, marker components
2	Entities	spawn / despawn, Entity handles, archetype formation
3	Systems	@System methods, class registration, single-instance rule
4	Queries — @Read and @Write	The hot loop API, Mut<C>, Entity parameters
5	Resources	Res<R>, ResMut<R>, per-world singletons
6	Change detection	@Filter(Added) / @Filter(Changed), dirty lists
7	RemovedComponents	Reacting to deletes with per-reader watermarks
8	Commands — deferred edits	Spawn/despawn from inside parallel systems

Advanced

#	Chapter	What you'll learn
9	Events	EventReader<E> / EventWriter<E>, double buffering
10	Local<T>	Per-system persistent mutable state
11	Stages and ordering	Default stages, before / after, @SystemSet
12	Multi-threading	Executors.multiThreaded(), disjoint-access DAG parallelism
13	Query filters — @With / @Without	Narrow archetype matches without binding
14	Field filters — @Where	Per-entity value predicates (and the tier-2 fallback)
15	@Exclusive systems	Single-threaded bulk edits, the tier-1 exclusive runner
16	Run conditions	@RunCondition / @RunIf for gating systems

Relations

#	Chapter	What you'll learn
17	Overview	What relations are, forward + reverse indices, @Relation
18	@Pair and PairReader	Set-oriented dispatch, fromSource / withTarget
19	@ForEachPair and @FromTarget	Tuple-oriented dispatch, tier-1 bytecode generation
20	Cleanup policies	RELEASE_TARGET vs CASCADE_SOURCE on despawn
21	RemovedRelations	Reacting to dropped pairs
22	Predator / prey example	Everything end-to-end on a real workload

If you're in a hurry

• Just want to write a physics loop? Read chapters 1–4 and you're done.
• Need change detection? Add chapters 6–7.
• Need cross-system coordination? Add chapter 8 (Commands) and chapter 11 (stages).
• Running multiple cores? Chapter 12 (multi-threading) is stand-alone.
• Building a graph of related entities (parent/child, hunter/prey, ally/enemy)? Jump straight to the relations section — chapters 17–22.