This started as “One File, Two Classes”, an experiment log from my Java practice repo, and I thought y’all might enjoy it!

Index

• Use Cases
• Experiment Results
• IDE Errors
• Next Steps

Use Cases

This bad idea (2 classes in one file) is a functionality test, as I thought of a couple narrow reasons why I might want to do this:

• It allows me to write fast iterative code with proper class structure, without messing around with renaming files, declaring/redeclaring/cleaning up dependencies, and all the rest of the busywork. Once structure has been figured out for the most part, classes can be separated into their own files.

• It’s great for code challenges where you still want to practice proper class structure without the hassle of compiling to bytecode.

Experiment Results

Works for execution, but not compilation.

For most Java programs (any Java program with more than 1 file, each containing a class, one of which has a main()), compliation to bytecode is required for execution.

javac ./folder_containing_2files/*

java main

For that scenario, running java main without compilation results in cannot find symbol errors.

However, in scenarios where there is only one class (containing your main()), the code can be executed without compilation. While this would fail if the file references a class in another file, interestingly, use of java standard library imports seem to work just fine. So do other classes added within the same file!

IDE Errors

Writing this in VS Code with a basic Extension Pack for Java installed, it says:

The public type Foober must be defined in its own file.

Should be defined in its own file? Sure! Reasonable. Must be? LIES! Or at least OpenJDK begs to differ.

Next Steps

Chances are there’s a practical reason to allow this execution behaviour beyond the use cases I’ve raised here. I might go look for them! Not sure. Honestly this whole experiment has been a tangent…