Interview questions on Concurrent Collections in java for experienced

  Part 4

Interview questions on Concurrent Collections in java for experienced covered in this post:

    Will it throw ConcurrentModificationException while iterating ConcurrentHashMap? If No Why?

-          While iterating ConcurrentHashMap it won’t throw ConcurrentModificationException.

-          Thread will get a bucket level or Segment level lock instead of a whole object lock.

-          Multiple threads are allowed to perform a thread-safe operation at a time.

-          Read operation can perform without lock and the write operation can perform by getting bucket level or Segment level lock.

-          When one thread is performing a read operation other threads are allowed to perform a write operation on the same object still you won’t get ConcurrentModificationException.

-          Please refer to the below example. Please cross verify with the above example as well.

package simplifiedjava.crackedInterview;  import java.util.Iterator; import java.util.Map; import java.util.concurrent.ConcurrentHashMap;  public class ConcurrentModificationExceptionDemo {        public static void main(String[] args) {             ConcurrentHashMap<Integer,String> m = new ConcurrentHashMap<Integer,String>();             m.put(101,"Shweta");             m.put(102,"Shruti");                        Iterator itr = m.entrySet().iterator();             while(itr.hasNext()) {                   m.put(103, "Anjali");                   Map.Entry<Integer, String> pair = (Map.Entry<Integer, String>)itr.next();                                         System.out.println("Key = "+ pair.getKey()+ "\t Value = "+ pair.getValue());             }                 } } Output: Key = 101     Value = Shweta Key = 102     Value = Shruti Key = 103      Value = Anjali

 

    What will happen while iterating any collection object including map trying to perform some operations like read or write on the object?

-          It will throw ConcurrentModificationException.

-          For more details, you may refer last 5 questions.

    Iterator of Concurrent Collection object is Fail Safe or Fail Fast?

-          Iterators of Concurrent Collections are Fail-Safe.

-          Fail-safe means iterator doesn’t fail if you are trying to modify the element at the time of iteration.

-          The Iterator will not fail while updating Concurrent Collection objects at the time of iteration.

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    Can I perform remove operation while iterating CopyOnWriteArrayList object?

-          We cannot perform the remove operation while iterating the CopyOnWriteArraylist object.

-          It is possible for List implementations.

 

    What will happen if I am trying to perform remove operation while iterating CopyOnWriteArrayList?

-          If we are trying to perform a remove operation while iterating CopyOnWriteArrayList, it will throw UnSupportedOperationException.

-          Please refer to the bleow example.

package simplifiedjava.crackedInterview;  import java.util.Iterator; import java.util.concurrent.CopyOnWriteArrayList;  public class CopyOnWriteArrayListDemo {        public static void main(String[] args) {             CopyOnWriteArrayList<Integer> list = new CopyOnWriteArrayList<Integer>();             list.add(10);             list.add(20);             list.add(30);             list.add(40);             list.add(50);                        Iterator itr = list.iterator();             while(itr.hasNext()) {                   System.out.println(itr.next());                   itr.remove();             }                 } } Output: 10 Exception in thread "main" java.lang.UnsupportedOperationException        at java.util.concurrent.CopyOnWriteArrayList$COWIterator.remove(Unknown Source)                at simplifiedjava.crackedInterview.CopyOnWriteArrayListDemo.main(CopyOnWriteArrayListDemo.java:19)

 

• Java interview questions and answers all MNC - Click here

• Basic core java interview questions and answers for freshers - Click here

• Core java interview questions for 3 years experience - Click here

• Core java interview questions and answers for 3-5 years exp - Click here

• Core java interview questions and Answers for 5 - 7 Years exp - Click here

• Basic Java Interview Questions and Answers - Click here

• Java interview questions and answers on oops - Click here

• Java interview questions and answers on Strings - Click here

• Java interview questions on exception handling - Click here

• Interview questions on multithreading in java for experienced - Click here

• Interview questions on serialization in java for experienced - Click here

• Interview questions on inner class in java for experienced - Click here

• Interview questions on Collections in java for experienced - Click here

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