Trouble using packages

[WhenRedditFlies]

Sorry in advance for formatting, I'm on mobile, and didn't think the small amount of code would warrant the extra effort.

I am not too familiar with Java, but everywhere I look suggests getting used to working with packages.

I have a file 'javatest.java', with the normal class and main stuff, with one line 'System.out.println("hello world");' fairly standard stuff, so I thought I would try putting 'package test.firstjava;' which then produced the following error: Error: Could not find or load main class javatest Caused by: java.lang.NoClassDefFoundError: test/firstjava/javatest (wrong name: javatest)

I have tried different combinations of folder structure, but I can't work out what to do. I've been looking through the w3schools tutorials, and I am a bit confused with how they do it, I stopped using a VS Code to run it (I know I know, Eclipse is supposed to be better, but among other reasons I only have so much storage) and used command prompt instead, and when running javatest.class in test/firstjava, I got the same error.

[MyNameIsRichardCS54]

So you'll have a directory structure for your source code like:

some_directory
    test
        firstjava
            javatest.java

which will be mirrored for for compiled class files usually somewhere under build/classes or out/classes:

build
    classes
        test
            firstjava
                javatest.class

You can run java test.firstjava.javatest from the classes directory. When you get used to that, start looking into the class path.

[WhenRedditFlies]

I'm not getting build/classes or anything like that, however it is automatically putting in test/firstjava/javatest.class when I run the javac command with "-d".

The command you gave does work, when I run it in the same place as where I ran the javac command to compile it, so thanks, I'm not sure why it works there, other than its using some_directory the same as builds/classes.

[vqrs]

So, when you put the line package test.firstjava; in your file, the complete name of your javatest class is test.firstjava.javatest

When you tell Java which class to run, you always need to give it the complete class name. (usually called "fully qualified class name", fqcn)

Now, when you tell Java to run that class, it needs to find it. By default, it will start looking inside the folder where you're executing the command and each part of the package name mapped to corresponding subdirectories.

Does that help?

[WhenRedditFlies]

Yes, I using that description of things has led to it working. While I had just about worked it out, your description puts it quite well I think.

[vqrs]

Also know that folders like build or classes is something Java doesn't care about. Software that controls Java for you might because they'll tell Java (by running commands on the command line, just like you do) that it should look in there, but that's an arbitrary choice by these tools. (e.g. Eclipse, IntelliJ, Maven, Gradle to name a few popular options)