What is internal (C#) or Package-Private (Java)? Why is it useful?
Module and Package-Level Visibility
C# internal and Java package-private provide visibility that is narrower than public but broader than private. In C#, internal makes a type or member accessible within the same assembly. In Java, package-private means no access modifier is specified and access is allowed within the same package. These mechanisms are useful for keeping implementation details inside a module while exposing only a smaller public API.
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C# internal is assembly-level visibility.
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Java package-private is package-level visibility.
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Both can hide implementation details from external consumers.
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They help define module boundaries and reduce public API surface.
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C# also provides InternalsVisibleTo for controlled access to internal members by specified friend assemblies.
Follow-up Questions
- What is an assembly in C#?
- What is package-private in Java?
- How can tests access internal C# members?
- How do module boundaries improve encapsulation?