Using Java14 to manually compile the module, but an error is reported

Question

I wrote a very simple Example of a Java module following the tutorial, but when using the javac command, I didn't get an error, and when compiling with the Java command, I got an error: Error occurred during initialization of boot layer java.lang.module.FindException: Module hellomod not found At present I do not know how to do, completely according to the tutorial to write, but run up an error, prompt can not find the module!

Using the javac command: javac hellomod/src/module-info.java hellomod/src/com/horstmann/hello/HelloWorld.java

Using the Java command: java -p hellomod -m hellomod/src/com.horstmann.hello.HelloWorld

The directory structure looks like this:

JavaPractice
----hellomod
--------src
------------com.horstmann.hello
----------------HelloWorld
------------module-info.java
---------hellomod.iml

The editor used is IntelliJ IDEA Educational Edition, How can I properly use a manually compiled module?