A tutorial written for Java 8 in 2015 still compiles and runs correctly today. Why does that backward compatibility hold across a decade, and why doesn't "a new Java version every six months" mean constant forced upgrades for a production team?

Java has been strongly backward compatible since 1996 — old code generally still compiles and runs on a new JVM, which is why a 2015 tutorial's code still works even though it's not how anyone writes idiomatic Java today. The six-month cadence (which started with Java 9) doesn't mean six-month upgrades either: most releases in between are supported only until the next one arrives, but a handful are designated long-term support (LTS) — 8, 11, 17, 21, 25 — and get years of security patches. Production teams sit on an LTS and move between LTS releases roughly every two years, not every six months; the frequent releases are where new features show up early, on something that isn't paying anyone's salary yet.