How do their APIs compare?

I should clarify: neither of these repositories exposes a conventional "API" in the sense of a web/network service API. They're fundamentally different kinds of projects, so a direct API comparison doesn't really apply. Let me lay out what each actually is.

beemdevelopment/aegis is an Android application (2FA/TOTP-HOTP authenticator), not a service with a public API. What it has instead are:

• Internal Java class APIs — e.g. SCrypt.generate(...) for key derivation in [app/src/main/java/com/beemdevelopment/aegis/crypto/bc/SCrypt.java:L37-L76], or Preferences methods like setIsBackupReminderNeeded/isBackupsReminderNeeded for managing app state in [app/src/main/java/com/beemdevelopment/aegis/Preferences.java:L513-L552].
• Enum-based utility APIs, like SortCategory, which exposes getComparator() and getMenuItem() to drive UI sorting logic [app/src/main/java/com/beemdevelopment/aegis/SortCategory.java:L12-L78].
• A documented vault file format (mentioned in the README) rather than a runtime API — this is the interface other tools/importers interact with, described in docs/vault.md.

So "API" here means internal, in-process Java interfaces used across the app's own modules (crypto, preferences, UI helpers), not something external clients call over a network.

hollischuang/tobetopjavaer isn't a software project at all — it's a documentation/knowledge-base repo (Java learning notes, e.g. articles on JVM class loading and SPI in [docs/basement/jvm/spi-parents-delegate.md:L1-L35], or API vs. SPI concepts in [docs/basics/java-basic/api-vs-spi.md:L1-L10]). It has no source code APIs of its own to compare — its content is about API/SPI concepts in Java generally (e.g. distinguishing API as "implementer defines interface, caller has no choice of implementation" vs. SPI as "caller defines interface, implementers plug in").

Bottom line: There's no apples-to-apples API comparison possible. Aegis has real internal Java APIs serving a live Android app; tobetopjavaer is educational content that discusses API/SPI as a general Java concept but doesn't implement any itself.