Java build failures — Unsupported class file major version

Log signatures

Unsupported class file major version 65
Could not determine java version
Could not resolve dependencies
cannot find symbol
BUILD FAILED

What’s happening

The two most diagnostic signatures here are version-skew tells: "Unsupported class file major version" means bytecode compiled by a newer JDK is being read by an older one (major 61 = Java 17, 65 = Java 21, 69 = Java 25 — the number names the culprit); "Could not determine java version" is usually an old Gradle that can't parse a new JDK's version string. "cannot find symbol" / "package does not exist" are compile errors — but when they appear en masse right after dependency lines, the real cause is upstream: a dependency that failed to resolve ("Could not resolve dependencies"), so every import from it "doesn't exist." "No tests found for given includes" means your test filter matched nothing — often a renamed test class with a stale CI filter.

Fix playbook

1. 1Find the first "Could not resolve" line. If present, fix resolution first — ignore the hundreds of "cannot find symbol" errors below it; they're shadows.
2. 2Version skew: align JDK across toolchain — java -version in CI vs sourceCompatibility/targetCompatibility/toolchain block. For Gradle, check the Gradle-vs-JDK compatibility matrix before bumping either.
3. 3Genuine COMPILATION ERROR with resolution healthy: ordinary code fix at the first reported file:line.
4. 4No tests found for given includes: fix the include filter or the test class naming; this fails builds on most configs and is pure configuration.
5. 5Rerun the single failing task/goal, not the whole lifecycle: ./gradlew :module:test / mvn -pl module test.