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Interview Questions and Answers for 'Concur' - 32 question(s) found - Order By Newest

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Almost sure to be asked in every company using any Dependency Injection framework ( Spring, Guice etc )
  Q1. What is Dependency Injection or IOC ( Inversion of Control ) ?Design
Ans. It is a Design Pattern that facilitates loose coupling by sending the dependency information ( object references of dependent object ) while building the state of the object. Objects are designed in a manner where they receive instances of the objects from other pieces of code, instead of constructing them internally and hence provide better flexibility.

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   Like         Discuss         Correct / Improve     design patterns   ioc ( Inversion of Control )  dependency injection     Asked in 83 Companies      intermediate        frequent


Frequently asked to fresh graduates and less experienced developers.
 Q2. Explain multithreading in Java ?Core Java
Ans. 1. Multithreading provides better interaction with the user by distribution of task

2. Threads in Java appear to run concurrently, so it provides simulation for simultaneous activities.The processor runs each thread for a short time and switches among the threads to simulate sim-ultaneous execution (context-switching) and it make appears that each thread has its own processor.By using this feature, users can make it appear as if multiple tasks are occurring simultaneously when, in fact, each is running for only a brief time before the context is switched to the next thread.

3. We can do other things while waiting for slow I/O operations.In the java.iopackage, the class InputStreamhas a method, read(), that blocks until a byte is read from the stream or until an IOExceptionis thrown. The thread that executes this method cannot do anything elsewhile awaiting the arrival of another byte on the stream.

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   Like         Discuss         Correct / Improve     java   threads   multi threading  concurrency   multithreading     Asked in 5 Companies      intermediate        frequent

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Frequently asked to fresh graduates.
  Q3. What is a Deadlock ?Operating System
Ans. When two threads are waiting each other and cant precede the program is said to be deadlock.

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   Like         Discuss         Correct / Improve     java   threads   multi threading   operating system   deadlock  concurrency     Asked in 23 Companies      basic        frequent


 Q4. What is a ConcurrentHashMap ?Core Java
Ans. ConcurrentHashMap is a hashMap that allows concurrent modifications from multiple threads as there can be multiple locks on the same hashmap.

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   Like         Discuss         Correct / Improve     java   collections   hashmap   map   concurrenthashmap   concurrenthashmap  concurrency   general electric   ge     Asked in 32 Companies        rare


 Q5. What is race condition ?Operating System
Ans. A source of possible errors in parallel programming, where one thread can cause an error in another thread by changing some aspect of the state of the program that the second thread is depending on (such as the value of variable).

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   Like         Discuss         Correct / Improve     java.threads   multithreading   race condition   parallel programming   synchronization   ebay   concurrency     Asked in 10 Companies


 Q6. What is ConcurrentModificationException ?Core Java
Ans. This is the exception that is thrown when we try to modify the non concurrent collection class while iterating through it.

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   Like         Discuss         Correct / Improve     java   collections   concurrentmodificationexception   exception  concurrency     Asked in 14 Companies      intermediate


 Q7. What is the use of runnable interface if we can always create a new thread using Thread class ?Core Java
Ans. It's a choice to be made whether to use first approach ( Thread class ) or second approach ( runnable interface ) by the programmer. The second facility has been given for cases where your class is already extending some parent class and hence cannot extend another class ( for Thread ) as Java doesn't allow multiple inheritance.

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   Like         Discuss         Correct / Improve     java   threads   multithreading   runnable interface  concurrency


 Q8. What is a BlockingQueue?Data Structures
Ans. BlockingQueue is a Queue that supports operations that wait for the queue to become non-empty when retrieving and removing an element, and wait for space to become available in the queue when adding an element.

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   Like         Discuss         Correct / Improve     blockingqueue   collections   java   concurrent collections     Asked in 10 Companies


 Q9. If you need to consume messages from the queue faster, which approach will you recommend - batching or concurrency ?Design
Ans. Each has it's own advantages

Batching requires less resources but may result in loosing whole batch in case of failure whereas concurrency even though is little more expensive in terms of resources but would result in minimal loss in case of failure.

In case messages are to be consumed in a particular order, batching them in that order and then consuming them makes better sense.

if incoming messages are not continuous , it makes more sense to do concurrency as we need not wait for all messages to form a batch and flush. Though time sensitivity can be added but that would add unnecessary complexity.

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   Like         Discuss         Correct / Improve     concurrency vs batching   concurrency  multithreading  batch


 Q10. What is concurrent interface ?Core Java
Ans. ConcurrentMap is an interface and it is a member of the Java Collections Framework. It represents a Map that is capable of handling concurrent access to it without affecting the consistency of entries in a map. ConcurrentMap interface present in java.util.concurrent package.

HashMap operations are not synchronized, while Hashtable provides synchronization. Though Hashtable is thread-safe, it is not very efficient. To solve this issue, the Java Collections Framework introduced ConcurrentMap in Java 1.5.

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   Like         Discuss         Correct / Improve     Concurrent Interface   java.util.concurrent   Java 8 Concurrency   java concurrency   java 8     Asked in 1 Companies


 Q11. When you will synchronize a piece of your code?
Ans. When you expect your code will be accessed by different threads and these threads may change a particular data causing data corruption.

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   Like         Discuss         Correct / Improve     java   threads   multi threading   synchronization   concurrency      basic        frequent


 Q12. What is ConcurrentLinkedDeque ?Core Java
Ans. It's a Collections concrete class that provides implementation of a Double Ended queue that allows concurrent insertion, removal, and access operations that can be executed safely across multiple threads.

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   Like         Discuss         Correct / Improve     java   collections   queue   deque   concurrent collections


 Q13. What is CopyOnWriteArrayList ?
Ans. Its a type of ArrayList in which all Write operations , i.e add and set are performed by creating a new copy. This array never changes during the lifetime of the iterator, so it never throws ConcurrentModificationException

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   Like         Discuss         Correct / Improve     java   collections   list   arraylist   copyonwritearraylist   ConcurrentModificationException     Asked in 1 Companies


 Q14. What are the advantages and disadvantages of CopyOnWriteArrayList ?Core Java
Ans. This collections class has been implemented in such a manner that it can never throw ConcurrentModificationException. As it performs update and write operations by creating a new copy of ArrayList, It's slower compared to ArrayList.

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   Like         Discuss         Correct / Improve     java   collections   list   arraylist   copyonwritearraylist   advantages-disadvantages   ConcurrentModificationException     Asked in 4 Companies      Expert


 Q15. Name few Concurrent Collection Classes ?
Ans. ConcurrentHashMap
ConcurrentLinkedDeque
ConcurrentLinkedQueue
ConcurrentMap
ConcurrentNavigableMap
ConcurrentSkipListMap
ConcurrentSkipListSet

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   Like         Discuss         Correct / Improve     java   collections   concurrent collections


  Q16. Explain the challenging problems you faced recently and how you overcame it ?General
Ans. [Open Ended Answer]

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   Like         Discuss         Correct / Improve     elsevier   open ended questions   overstock.com   cerner     Asked in 15 Companies        frequent


 Q17. What is the use of Synchronized block ?Core Java
Ans. The goal of a synchronised block is to achieve mutual exclusion i.e at one time, the segment of the code should be executed by single thread only and hence the lock needs to be retrieved before executing the segment and then released.

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   Like         Discuss         Correct / Improve     synchronized block   synchronized   synchronization   multithreading   threads   mutual exclusion   concurrency     Asked in 4 Companies      intermediate        frequent

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 Q18. Difference between concurrentHashMap and HashTable ?Core Java
Ans. HashTable locks the complete collection to provide synchronization whereas ConcurrentHashMap only locks segments to achieve synchronization and hence better efficient and faster.

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   Like         Discuss         Correct / Improve     concurrentHashMap  HashTable  Map  Collections     Asked in 2 Companies


 Q19. isnt the use of HashTable and ConcurrentHashMap the same, i.e providing synchronized map collection ?Core Java
Ans. Yes, they both aim at providing synchronized access to the Map collection. The only difference is in their implementation. ConcurrentHashMap came after HashTable and hence technically more efficient as it doesn't lock the complete map while accessing it.

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   Like         Discuss         Correct / Improve     HashTable  ConcurrentHashMap  map  Collections


 Q20. How do threads share information ?Core Java
Ans. Through common memory area.

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   Like         Discuss         Correct / Improve     threads     Asked in 1 Companies


 Q21. What is the use of java.util.concurrent package in Java ?Core Java
 This question is still unanswered. Can you please provide an answer.


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   Like         Discuss         Correct / Improve     java.util.concurrent


 Q22. What are the advantages and disadvantages of using lock classes from java.util.concurrent.locks vs. synchronized methods ?Core Java
Ans. http://www.devinline.com/2015/10/Lock-Vs-synchronized-in-java.html

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   Like         Discuss         Correct / Improve     java.util.concurrent.locks  synchronization  synchronized methods


 Q23. Explain Java 8 concurrency mechanism.Core Java
 This question was recently asked at 'IBM'.This question is still unanswered. Can you please provide an answer.


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   Like         Discuss         Correct / Improve     synchronization  concurrency  java 8  java8     Asked in 1 Companies


 Q24. If a Map needs to be accessed simultaneously by multiple threads, which collection class should be used ? Core Java
Ans. ConcurrentHashMap

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   Like         Discuss         Correct / Improve     map  concurrenthashmap  multithreading


 Q25. Which are the thread safe / synchronized / concurrent classes in java collections ?Core Java
Ans. Stack
Properties
Vector
BlockingQueue
ConcurrentMap
ConcurrentNavigableMap

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   Like         Discuss         Correct / Improve     collections  concurrent classes


 Q26. What are the different ways to avoid multi Threading related problems in Java ?Core Java
Ans. Synchronization,
Concurrent classes,
Volatile keyword,
Implementing concurrent Lock interface,
Immutable classes

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   Like         Discuss         Correct / Improve     multithreading  threads  ways to avoid thread related problems  synchronization  volatile  concurrent collections      Intermediate


 Q27. What is Lock interface in Java Concurrency API ?Core Java
Ans. Lock interface provide more extensive locking. They allow more flexible structuring and may support multiple associated Condition objects.

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   Like         Discuss         Correct / Improve     concurrency api


 Q28. Why Concurrent Collection Classes are fail-fast in Java ?Core Java
 This question is still unanswered. Can you please provide an answer.


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   Like         Discuss         Correct / Improve     concurrent collection classes   fail fast   fail-fast  collections  collection classes      expert


 Q29. Are arrays Thread Safe ?Core Java
Ans. Yes

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   Like         Discuss         Correct / Improve     arrays  concurrency     Asked in 1 Companies


 Q30. Isnt the use of HashTable and ConcurrentHashMap the same, i.e providing synchronized map collection ?Core Java
Ans. Both provide the thread safety but the actual difference come when talk about performance. CHM gives best performance when no of writer threads are less in number.

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   Like         Discuss         Correct / Improve     synchronized collections  hashtable  ConcurrentHashMap     Asked in 1 Companies


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