Stuff Isn't working. How do I explain....

Helloooo! Im making a mod. this is the link to the forum. Im making a fish, but it comes up with this error:

> Task :compileJava FAILED
FAILURE: Build failed with an exception.
* What went wrong:
Execution failed for task ':compileJava'.
> Compilation failed; see the compiler error output for details.
* Try:
> Run with --stacktrace option to get the stack trace.
> Run with --info or --debug option to get more log output.
> Run with --scan to get full insights.
* Get more help at https://help.gradle.org
BUILD FAILED in 22s
1 actionable task: 1 executed

BUILD FAILED
Task completed in 1 minute

I dont know how id find this, so im asking instead of someone else.