Step-by-Step Explanation: Kotlin Visibility Modifiers

Kotlin provides a robust set of visibility modifiers designed to improve encapsulation and modularity.

1. The Four Modifiers

1. public (Default): Visible everywhere.
2. private:
   • At top-level: Visible only within the file.
   • Inside a class: Visible only within the class.
3. internal: Visible only within the same module (e.g., a Gradle source set). This is a powerful tool for building libraries.
4. protected:
   • Visible only within the class and its subclasses.
   • Crucial Difference: Unlike Java, protected in Kotlin does NOT grant access to other classes in the same package.

2. Top-level Visibility

You can control the visibility of classes, functions, and properties defined directly in a package. - private is great for utility functions used only within one file. - internal allows you to hide implementation details from users of your library while keeping them accessible across your own project's files.

3. Class and Interface Members

Visibility modifiers inside classes work similarly to Java but with the stricter protected and the addition of internal. - Note: An outer class does not see private members of its inner or nested classes.

4. Constructor Visibility

To hide a primary constructor, you must use the constructor keyword explicitly:

class User private constructor(val name: String)

This is often used in conjunction with a companion object factory or the Builder pattern.

5. Local Declarations

Local variables and functions (defined inside a method) cannot have visibility modifiers. Their scope is always restricted to the block where they are declared.

6. Verification

Verified by building the project. The implementation showed that internal properties are accessible within the module, while private top-level functions are hidden from other files.