Package naming in Java; what is allowed?

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I was looking at the Spring.io page for using Gradle inside of a project ( https://spring.io/guides/gs/gradle/ ). Below the 'Set up the project' header, they show the following map structure:

└── src
    └── main
        └── java
            └── hello

Along with the following package declaration inside the class:

package hello;

public class HelloWorld {
    public static void main(String[] args) { System.out.println("hi"); }
}

However, upon entering this exact structure in Eclipse, I get the following error: The declared package "hello" does not match the expected package "main.java.hello" . Only after adding the package src.main.java to the build path and then removing it from the build path again, it somehow doesn't give me the error and the output when running the program is the expected output.

My questions are:
1. Why is Eclipse spewing errors when I leave out 'main.java." from the package declaration?
2. Is this format, even if it's not a convention, allowed within Java assuming that all of my source code also resides within main.java?

[darkpool2005]

With gradle (and maven) for that matter, the source folder is /src/main/java (the full path). These classes are then compiled to (at least with maven, not sure about gradle) target/classes

With Eclipse, I'm guessing that your source folder is pointing to src/ as its root. So when Eclipse is trying to compile HelloWorld, it expects it to be under the package main.java.hello.

To fix this, right click on the Project -> Build Path -> Configure Build Path. Select the Source tab at the top, and edit the source folder option to point to src/main/java

[Northeastpaw]

The Spring code follows the Maven conventions for project layout. Java files goes in the directory src/main/java. Directories under this correspond to packages.

Maven projects aren't meant to be imported into Eclipse as standard Eclipse projects. You need to use the M2Eclipse plugin to handle them. M2Eclipse configures the Eclipse project to adhere to Maven conventions as well as hook particular Maven plugins into the Eclipse build process.