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Blog: Keeping Secrets - Visibility Modifiers in Kotlin

Blog: Keeping Secrets - Visibility Modifiers in Kotlin

Day 21! Today I explored the walls we build around our code: Visibility Modifiers.

Public by Default

In Java, if you don't specify visibility, it’s "package-private." In Kotlin, the default is public. This reflects Kotlin's philosophy of being "concise by default"—most of the time, you want your code to be accessible, so you don't have to type public everywhere.

The "Internal" Revolution

My favorite discovery today was the internal modifier. In Java, it's notoriously hard to hide code from your library's users without putting everything in one giant package. Kotlin solves this with internal, which makes code visible to your entire module but invisible to anyone who imports your library. It’s a game-changer for clean API design.

Stricter Protected

Kotlin’s protected is stricter than Java’s. In Java, protected also means "accessible to the whole package." Kotlin says: "No, if you aren't a subclass, you shouldn't see this." This makes inheritance hierarchies much more predictable and secure.

Private at the Top

I also learned that you can have private functions at the top level of a file. This is perfect for "helper" logic that doesn't need its own class but shouldn't be exposed to the rest of the project. It keeps your namespace clean.

Hidden Constructors

Need to force users to use a factory method? Just mark your primary constructor as private. Kotlin makes this syntax very clear, though you do have to add the constructor keyword explicitly.

Conclusion

Visibility modifiers in Kotlin aren't just about hiding code; they are about intent. They let you define exactly who should be able to see and use your logic, leading to more maintainable and less brittle systems.

Check out the full technical breakdown!

Kotlin #VisibilityModifiers #Encapsulation #CleanCode #AndroidDev #ModuleScope #SoftwareArchitecture

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