Notes on Final Keyword in Java

Introduction to Final Keyword

• The final keyword is significant in Java, signifying 'constant' or 'unchangeable'.

Key Points About Final Keyword

1. Final for Variables

   • A final variable cannot have its value changed after initialization.
   • Can be initialized in the constructor if not done at declaration.
   • Example: final int a = 10; (cannot change a after initialization).

2. Final for Methods

   • A final method cannot be overridden by subclasses.
   • Use it to prevent method modification.

3. Final for Classes

   • A final class cannot be inherited or extended.
   • Prevents modification of the class structure.

Common Interview Questions and Answers

1. What does the final keyword mean?

   • Represents constants; signifying that the value cannot be changed.

2. How to prevent a class from being inherited?

   • Make the class final.

3. How to prevent a method from being inherited?

   • Make the method final or declare the class final.

4. How to prevent variables from being altered?

   • Make the variable final to prevent new assignments.
   • Example: Class A with final int a = 10; cannot change a.

5. What is a pure constant in Java?

   • final static variable; a single copy stored with unchangeable value.

6. Can you combine abstract, final, and public keywords in a class?

   • Yes, you can combine abstract and final but not in the same declaration since they conflict (one requires extension, the other forbids it).

7. Is it possible to declare a variable as both final and abstract?

   • No, because variables cannot be abstract.

8. Can you have a static final variable in Java?

   • Yes, these are termed as pure constants.
   • Common example: public final static int pi = 3.14;

9. Are there any inbuilt classes declared as final in Java?

   • Yes, all wrapper classes (e.g., Integer, Float) and the String class are final.

10. How does the final keyword contribute to the security and stability of Java?

    • Ensures that universal constants (like pi) remain unchanged, maintaining the integrity of the program.

Conclusion

• The final keyword plays a crucial role in ensuring constants, security, and stability in Java programming.
• Further discussions on more interview questions will continue in the next video. Thank you!