| Symptom | Fix |
|---|---|
Could not find or load main class |
IntelliJ didn’t load the Maven project — open the Maven tool window (View → Tool Windows → Maven) and click the refresh icon |
JDK 21 required or module not specified |
File → Project Structure → SDK — set it to JDK 24 |
| Window opens but game is blank | Press ENTER to start |
./mvnw: Permission denied |
Run chmod +x mvnw in the terminal, then retry |
WARNING: sun.misc.Unsafe in the console |
Harmless — ignore it. Comes from the graphics library, not your code |
./mvnw javafx:run on one machine before class to warm up the Maven
cache, then copy ~/.m2 to other machines if the school network blocks
Maven Central.