package in .java file makes class file unuseable

Question

It\'s been too long since I\'ve last done Java, and I can\'t remember why the following happens:

Given this file, created by a standard Maven project, as can be seen her

Answer 1

This is because in Java filesystem files map to classes (e.g. each public class must be in a separate eponymous file) and packages map to directories.

So if you have a class which is in the com.mycompany.app package it must be in com/mycompany/app directory relative to the classpath.

In your case you should have an output directory, say and the you should have the class in /com/mycompany/app/App.java. Then you build it, running javac from and giving com/mycompany/app/App.java as parameter, instead of com/mycompany/app/App.java.

Running the class works in an analogical way, but you give the fully-qualified-name of the class, instead of the directory path.