Core Java interview Questions

1.    What is the difference between object and class?

2.    What is difference between overloading and overriding?

3.    What is aggregation and Composition?

4.    What is difference between abstract class and interface?

5.    How will you create an object without using 'new' operator?

6.    Explain about Thread life cycle?

7.    What is difference between StringBuffer and StringBuilder?

8.    What is hashcode?

9.    Explain the use of synchronization block

10. How will make a method() Thread-safe

11. Explain about Serializable and Externalizable interface

12.  Explain Object comparison using ‘==’ and equals() method

13.  When will go for LinkedList vs ArrayList

14. What is static method and static block ?

15. When will you use Hashmap vs TreeMap?

16.  What are the types of exception in java

17.  Write a code snippet for singleton design pattern

18.  What is multi-threading?

19. What is the difference between sleep() and wait() method

20.  How to call an external process in java

21.  What is Lambda expression?

22. What is Functional interface?

23. Difference between Iterator vs Enumeration vs Spliterator?

24. What is Priority Queue?

25.  What are types of Class Loaders available in Java

26. What is a Generic Type Parameter?

27. What is a Wildcard type?

28. What is an Upper Bounded Wildcard?

29. What is a Lower Bound Wildcard

30. What is an Unbounded Wildcard?

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