This started as “One File, Two Classes”, an experiment log in Java practice repo, and I thought y’all might enjoy it!
Index
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:
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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.
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It’s great for code challenges where you still wanna practice good 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…