patterns and frameworks question and answers with example sample code

I am looking for help regarding my project, which requires a code sample and basic example in the Java programming language. Answer all the questions below. In your answer for each question explain with sample code or image whichever is preferable. 1. What are generics? 2. Can we change the scope of the overridden method in the subclass for private, public, default and protected? Explain how can it be changed for each scope? 3. What is the covariant return type? 4. Can we override the static and private methods? Why? 5. Difference between String Buffer and StringBuilder? 6. Difference between String class and String Buffer? 7. Can we declare constructor as final? 8. Can we have try without catch block in java? 9. What is try with the resource? 10. Can we modify the throws clause of the superclass method while overriding it in the subclass? 11. What is an association, aggregation, and composition in UML? 12. Difference between final, finally and finalize()? 13. Difference between Vector and ArrayList? 14. What are the different ways to make ArrayList methods synchronized? 15. Difference between Hash table and Hash Map? 16. In Java 8, explain how Hasp Map internally works? 17. Difference between fail fast and fail-safe iterator? 18. Can we start the thread twice? 19. What are the different ways to create a thread in java? Which one is preferred? 20. What are the different states a thread will go through? 21. What is Serialization? How do we achieve it? 22. What is immutable class? Is String class immutable? 23. Do immutable classes thread safe? If yes then how? 24. Can we call the garbage collector explicitly? Will it trigger the garbage collector? 25. What are Java 8 features? Explain all of them with examples? 26. How to make a pure singleton? 27. How to make a singleton synchronized?