How do their APIs compare?

These two repositories aren't really comparable at the API level, since they serve entirely different purposes — one is a study/reference collection, the other is a live software library with a real public API surface.

h2pl/javatutorial: no API — it's documentation

This repo has no source code API of its own. It's a curated Markdown knowledge base for Java interview/backend study, organized under docs/Java/ into topics like basics, collections, concurrency, and design patterns (per the README's table of contents). Any "code" you find here is illustrative snippets inside markdown files demonstrating standard JDK usage, e.g.:

• Custom Comparator implementations and Java 8 lambda-based comparators [docs/Java/collection/Java集合详解：Iterator，fail-fast机制与比较器.md:L552-L710]
• Notes on JDK design patterns like the Strategy pattern via Comparator#compare(), HttpServlet, Filter#doFilter() [docs/Java/design-parttern/初探Java设计模式：JDK中的设计模式.md:L290-L299]
• Java 8 feature walkthroughs (lambdas, functional interfaces) [docs/Java/basic/Java8新特性终极指南.md:L43-L122]
• AQS/lock internals explanation with annotated JDK source [docs/Java/concurrency/Java并发指南：JUC的核心类AQS详解.md:L160-L199]

So "its API" is really just references to and explanations of the standard Java API — there's nothing to version, deprecate, or design here. Also worth noting per the RepoPilot verdict: WAIT — Slowing, last commit 12mo ago, meaning this content is not actively maintained/updated.

reactivex/rxjava: a real, versioned reactive-programming API

RxJava exposes a substantial public API surface for reactive stream types, e.g.:

• Completable — a reactive type representing deferred computation with only completion/error signals, no value emission. It documents a strict emission protocol onSubscribe (onError | onComplete)? and factory methods like Completable.create(CompletableOnSubscribe) [src/main/java/io/reactivex/rxjava4/core/Completable.java:L1-L107, L348-L387].
• SchedulerSupport — an annotation (@Retention(RUNTIME), targeting constructors/methods/types) used across the public API to document which Scheduler an operator uses, with constants NONE and CUSTOM [src/main/java/io/reactivex/rxjava4/annotations/SchedulerSupport.java:L1-L40].
• A newer Streamable type (seen in JMH benchmarks like StreamableConcatIterablePerf and StreamableCollectPerf), which appears to be an in-development reactive abstraction being tuned for performance (avoiding wip counter decrements, avoiding whenComplete allocation, synchronous indexing/bias optimizations) [src/jmh/java/io/reactivex/rxjava4/streamable/StreamableCollectPerf.java:L1-L120].

RxJava's API is annotated (@CheckReturnValue, @NonNull, @SchedulerSupport), documented with Javadoc marble-diagram references, and backed by JMH performance benchmarks that track regressions/improvements numerically — a level of API rigor (nullability contracts, scheduler contracts, throughput benchmarking) that has no counterpart in javatutorial.

Summary of the comparison

Aspect	h2pl/javatutorial	reactivex/rxjava
Has a real API	No — markdown notes only	Yes — versioned reactive types (Completable, Streamable, etc.)
API contracts/annotations	None	@NonNull, @CheckReturnValue, @SchedulerSupport [src/main/java/io/reactivex/rxjava4/annotations/SchedulerSupport.java:L28-L39]
Performance tracking	None	JMH benchmarks with recorded throughput history [src/jmh/java/io/reactivex/rxjava4/streamable/StreamableCollectPerf.java:L1-L120]
Maintenance signal	RepoPilot: WAIT — slowing, 12mo since last commit	No maintenance verdict available in the provided data

If you want, I can dig de