Download link: 
➡ Click here: Java interview questions
In some cases volatile also provide atomicity e. You cannot override a private or static method in Java. The major difference between Heap and Stack memory are: Features Stack Heap Memory Stack memory is used only by one thread of execution. Spliterator stands for Splitable Iterator.
LogManager manages a set of individual loggers which are singletons. What is the difference between Elements and Stream in Java8. Immutable objects are those whose state cannot be changed once created. What purpose does the keywords final, finally, and finalize fulfill. We can use getResultSet to get the ResultSet and getUpdateCount method to retrieve the update count. In this process, an met method is called through the reference variable of a superclass. An Interface visibility must be public or none. If a class is not found in CLASSPATH then Java throws ClassNotFoundException. Gone are the days, when knowing the difference between String and StringBuffer can help you to go through the civil round of interview, questions are becoming more advanced java interview questions interviewers are asking more deep questions. For example, if two threads, A and B, both try to deposit 10 dollars to the same account, both might first call get to read the account balance, say 100 dollars, then they both add 10 jesus and put the sum of 110 dollars java interview questions the account; 10 dollars have now evaporated.
You cannot update Swing components e. Whereever we use Lambda Expressions that means we are using Functional Interfaces. This is the default scope for the spring beans. Can you write immutable object?
Java Interview Questions - Now let's see the answer. On the job you want people who are creative, capable of exploring available options, and capable of executing well on the tasks that they are assigned to them, large or small.
In this article, I am sharing 30 core Java technical questions, from screening and phone round of interviews. In telephonic interviews, questions are short, fact-based and Interviewer expects some keyword in answers. Accordingly, I have given very short answers to these question, only main points; just to make this as revision post. I am expecting every to know answers to all these Java technical questions if he has more than 4 to 5 years experience. I have tried to include all classical and hugely popular, frequently asked questions from different topics like String, multi-threading, collection, design pattern, object-oriented design, garbage collection, generics and advanced Java concurrency questions. Since core Java interviewer's normally don't ask questions on JSP, Servlets, and other JEE technologies, I have not included them in this list. The sole purpose of this list is to give freshers and less experienced developers an idea of what kind of core Java technical questions are asked on. For curious ones, I have also included links to more detail answers and discussions. I have not included questions based upon recent Java changes like Java 8, Java 9, and Java 10 e. That is a big list with more than 140+ questions from different topics and if you have some time in hand, you can use that to prepare well for your next Java interview. Java Phone Interview Questions Answers Anyway, without any further ado, here is a list of 30 frequently asked Java interview questions from telephonic round: 1. Why is String immutable in Java? Security, String pool implementation, see more 2. Can abstract class have a constructor in Java? Yes, detailed answer is 3. Which two methods are overridden by an Object, intended to be used as a key in HashMap? What is the difference between wait and sleep in Java? Difference between List and Set in Java? The list is ordered, allows duplicates and indexed, Set is unordered, don't allow duplicates, for a more detailed answer, see post 6. How do you make a class Immutable in Java? Make it final, final fields without a setter, the state is only set in the constructor, no leak of internal reference, copy data for mutable members, 7. Which data type you should use to represent currency in Java? You should answer long or BigDecimal, if you say double, you need to convince them about rounding and how do you avoid floating point issues. When to use abstract class and interface in Java? Use interface for type declaration, use an abstract class if evolution is a concern, for few more points, see post 9. Difference between Hashtable and HashMap in Java? Another, common Java question, former is thread-safe and doesn't allow null, later is not thread-safe, former is also slow because of the whole locking of Map, while HashMap is fast because of no locking, 10. What is the difference between ArrayList and LinkedList in Java? It covers all important topics including core Java, data structure and algorithm, frameworks like Spring and Hibernate, JDBC, JUnit, Design patterns, Android, Scala and advanced concurrency stuff for experienced programmers. Anyway, let's move on to the next question 11. What is the difference between Overloading and Overriding in Java? What kind of reference types are exists in Java? Strong reference, Weak references, Soft reference and Phantom reference. Except strong, all other reference allows the object to be garbage collected. For example, if an object hash only weak reference, then it's eligible for GC if the program needs space 13. Difference between checked and unchecked exception in Java? Later is not checked by the compiler but can be caught using try-catch or try-finally block. SQLException is checked exception, while java. ArrayIndexOutOfBoundsException is an example of the unchecked exception in Java, for better answer see 14. Does Java array is an instance of Object? Does List can hold Integers? Yes, because Integer is a subclass of Number and generics allows that, 16. Can we pass ArrayList to a method which accepts List in Java? Yes, Again this is a tricky question and you need in-depth knowledge of Generics to answer this question. If you want to know more about Generics I suggest you join the course on Udemy. One of the best resource to learn Java in-depth. Can we pass ArrayList to a method which accepts List? No How to fix that? List to know more about bounded and unbounded wildcards and other generics questions see this 18. What is a volatile variable in Java? It guarantees happens-before relationship, variable's value is read into main memory, for detail answer see 19. What is the difference between CountDownLatch and CyclicBarrier in Java? Both are concurrency utility classes introduced in Java 5 and can be used to wait for other threads to finish their job before starting itself. The key difference between CountDownLatch and CyclicBarrier is that former cannot be reused once the count reaches zero while later can be reused even after the barrier is broken, for in-depth discussion, see post 20. Does BlockingQueue is thread-safe in Java? Yes, take and put method of this class guarantees thread-safety, no need to externally synchronize this class for adding and retrieving objects, here is an example of this class to solve 21. Why wait and notify method should be called in a loop? This can be really difficult to answer if you have never used wait-notify because it seems pretty logical that an if-else block can be used but that would be wrong. As Joshua Bloch mentioned in his classic book, we should always call wai-notify in the loop to prevent doing the task, if a condition is not true and the thread is awake due to false alarms, checking conditions in loop ensures that processing is only done when business logic allows. If you haven't read that book yet, I highly recommend it. A is also out and it's available on 50% discount at the time of writing. This is again a tricky question and common idiom to avoid NullPointerException in Java. What is marker or tag interface in Java? An interface, which presence means an instruction for JVM or compiler e. Serializable, from Java 5 onwards Annotation is better suited for this job, to learn more and answer in detail see this 24. What is the difference between the Serializable and Externalizable interface in Java? This is another popular Java question. The Externalizable interface provides more control over serialization process, and allow you to define a custom binary format for your object, later is also suited for performance-sensitive application, see for more details 25. Can Enum types implement interface in Java? Can Enum extend a class in Java? No, because Java allows a class to only extend one class and enum by default extends java. Enum, see here for more 27. How to prevent your class from being subclassed? Make it final or make constructor private, for curious developers are three technical ways to prevent your class from being subclassed. Can we override a static method in Java? No, it can only be hidden, no compilation error, see for more details 29. Which design pattern have you used recently? You can answer this question based upon experience but you should give any example except Singleton and MVC e. Decorator, Strategy or Factory pattern to make a better impression. If you don't know about design patterns then you can check course by Loony Corn, an ex-Google, and Stanford. What is the difference between StringBuffer and StringBuilder in Java? Another very common questions, which is mostly asked, beginners. The short answer is that former is synchronized, and slow, while later is not synchronized and fast, for more details see post That's all on this list of 30 core Java technical questions asked in phone interviews to freshers, junior Java developers and Java programmers up-to experience ranging from 1 to 2 years. As I said before, use this list for quick revision, especially if you are in hurry. Give short, to-the-point and specific answers, until Interviewer asks for more or insist to elaborate by asking follow-up questions. Since most of the phone interviews are done to screen candidates, mostly similar questions are asked of all candidates. By the way, always do a short research on the company before your phone interview, you might find some of the questions previously asked on Google itself. Further Learning Thanks for reading this article so far. If you like these Java interview questions or have seen them on your telephonic round of interview then please share this post with your friends and colleagues on Facebook, Twitter, Email etc. If you have any questions or feedback, please drop a note. All the best Guys Anonymous For Core Java Developers, I would say to prepare well for DS and Algo, you can check some here, once you are good at that, just prepare some basic Java questions for telephonic round. Once you are done that you are ready, but if you want more confidence, you should check this , which contains core Java questions including multi-threading, exception handling, collections, GC, design pattern and OOP questions from last 5 years of Java interviews.