access modifier interview questions:

Basic Concepts

1. What are the four access modifiers in Java?

  • public – Accessible everywhere.
  • private – Accessible only within the same class.
  • protected – Accessible within the same package and by subclasses (even in different packages).
  • Default (package-private) – Accessible only within the same package (no explicit keyword).

2. Explain the differences between public, private, protected, and default access.

| Modifier | Class | Package | Subclass (same pkg) | Subclass (diff pkg) | World (anywhere) |
|--------------|-------|---------|---------------------|---------------------|------------------|
| public | ✅ | ✅ | ✅ | ✅ | ✅ |
| protected | ✅ | ✅ | ✅ | ✅ | ❌ |
| Default | ✅ | ✅ | ✅ | ❌ | ❌ |
| private | ✅ | ❌ | ❌ | ❌ | ❌ |

3. What is the default access modifier in Java when none is specified?

  • Default (package-private) – Only accessible within the same package.

4. Can you access a private method from another class?

  • No, private methods are accessible only within the same class.

Practical Application

5. When would you use private vs. public access modifiers?

  • Use private for encapsulation (hiding internal implementation).
  • Use public for methods/classes that need to be accessible globally (e.g., API methods).

6. Why would you make a class member protected instead of public or private?

  • protected allows subclasses to access the member while still restricting access from unrelated classes.

7. How does default (package-private) access differ from protected?

  • Default: Only accessible within the same package.
  • Protected: Accessible within the same package and by subclasses (even in different packages).

8. Can a subclass access its superclass's private members?

  • No, but it can access protected and public members.

Advanced Topics

9. Can access modifiers be applied to local variables?

  • No, local variables (inside methods/blocks) cannot have access modifiers. They are always local in scope.

10. How do access modifiers affect method overriding?

  • The overriding method cannot be more restrictive than the overridden method (e.g., cannot override a public method as private).

11. What happens if you try to override a method with a more restrictive access modifier?

  • Compilation error (e.g., overriding a public method as private is invalid).

12. Can interfaces have private methods? (Java 9+)

  • Yes, Java 9+ allows private methods in interfaces (for internal helper methods).

13. How do access modifiers work with nested classes?

  • Nested classes (static or non-static) can have any access modifier (public, private, protected, default).

Scenario-based Questions

14. If you want a method to be accessible only within its package and to subclasses (even in other packages), which access modifier would you use?

  • protected (since default only allows same-package access).

15. Why might you declare a class as package-private (no modifier)?

  • To restrict usage to the same package (e.g., utility classes not meant for external use).

16. How would you expose certain functionality of a class while keeping its implementation details hidden?

  • Use public methods for external access and private methods for internal logic (encapsulation).

Tricky Questions

17. Can a public class have private or protected members?

  • Yes, a public class can have any access modifier for its members (e.g., private fields, protected methods).

18. Is it possible to restrict access to a public method in a subclass?

  • No, you cannot make it more restrictive (e.g., cannot override public as private).

19. Can you change the access modifier when overriding a method?

  • Yes, but only to make it less restrictive (e.g., overriding a protected method as public is allowed).

20. Why can't a subclass method be more restrictive than its superclass method?

  • It would violate the Liskov Substitution Principle (a subclass should be usable wherever the superclass is expected).

Bonus: Common Mistakes

  • Assuming protected means only subclasses → It also allows same-package access.
  • Using default when protected is needed → default doesn’t allow subclass access from different packages.
  • Trying to use access modifiers on local variables → Not allowed.

Would you like a deeper explanation on any specific topic? 😊