As an Full Stack professional, it is essential to know the Core Java, learn the right technologies and prepare the right answers to commonly asked Core Java Interview Questions. Here’s a definitive list of top 50 Core Java Interview Questions.
Question 1.) What are wrapper classes in Java? Question 2.) What are constructors in Java? Question 3.) What is Multi-threading? Question 4.) What is Synchronization? Question 5.) What are access modifiers in Java? Question 6.) What is singleton class in Java and how can we make a class singleton Question 7.) What are the main concepts of OOPs in Java? Question 8.) What is the difference between Array list and vector in Java? Question 9.) What are the differences between Heap and Stack Memory in Java? Question 10.) What is the difference between a local variable and an instance variable? Question 11.) What is a package in Java? List down various advantages of packages. Question 12.) Why pointers are not used in Java? Question 13.) What is final keyword in Java? Question 14.) Difference between String, StringBuilder, and StringBuffer. Question 15.) What is the difference between this() and super() in Java? Question 16.) What is a classloader in Java? Question 17.) What is the difference between an array and an array list? Question 18.) What is collection class in Java? List down its methods and interfaces. Question 19.) What are the different methods of session management in servlets? Question 20.) Why is multiple inheritance not supported in java? Question 21.) Difference between method Overloading and Overriding. Question 22.) What is the static block? Question 23.) Can we execute a program without main() method? Question 24.)What is the difference between abstract classes and interfaces? Question 25.) Can you override a private or static method in Java? Question 26.) What is Java String Pool? Question 27.) Differentiate between static and non-static methods in Java. Question 28.) What is an object in Java and how is it created? Question 29.) What is Object Oriented Programming? Question 30.) How does Java enable high performance? Question 31.) Explain different types of typecasting? Question 31.) What are the default values for local variables? Question 33.) What is multiple inheritance? Does Java support multiple inheritance? If not, how can it be achieved? Question 34.) How do you make a thread in Java? Give examples. Question 35.) Why do we use the yield() method? Question 36.) Can you explain the thread lifecycle in Java? Question 37.) Please draw a comparison between notify() and notifyAll() methods. Question 38.) How will you distinguish processes from threads? Question 39.) Could you explain various types of Exceptions in Java? Also, tell us about the different ways of handling them. Question 40.) Write suitable code examples to demonstrate the use of final, final, and finalize. Question 41.) Let us know the Java Exception Hierarchy? Question 42.) Could you demonstrate how to delete a cookie in Servlet with a code example Question 43.) Which methods are used during the Serialization and Deserialization process? Question 44.) Can an interface implement or extend another interface? Question 45.) What is Marker interface? Question 46.) What is inner class in java? Question 47.) What is ternary operator in java? Question 48.) What is Garbage Collection? Question 49.) What is the use of System class? Question 50.) What is object cloning?
I hope these set of questions would help you to prepare for Core Java Interview.