Interview questions on Concurrent Collections in java for experienced

 Part 5

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

    What is the difference between ArrayList and CopyOnWriteArrayList?

	ArrayList	CopyOnWriteArrayList
1.	ArrayList is not thread-safe.	CopyOnWriteArrayList is thread-safe.
2.	In ArrayList, clone copy doesn’t create for every update operation.	In CopyOnWriteArrayList clone copy creates for each update operation.
3.	While executing one thread no other thread allowed accessing the same resources. If you try to modify then it will throw ConcurrentModificationException.	While executing one thread other threads are allowed to perform an operation on the same resources it won’t throw ConcurrentModificationException.
4.	Iterator is Fail-Fast.	Iterator is Fail-Safe.
5.	While traversing the list using iterator we can perform a remove operation.	While traversing CopyOnWriteArrayList using iterator we cannot perform removes operation otherwise, it will throw UnSupportedOperationException.

 

    What is the difference between CopyOnWriteArrayList and SynchronizedList?

	CopyOnWriteArrayList	SynchronizedList
1.	A new clone copy will be created for every update operation.	A new clone copy won’t create for every update operation.
2.	Multiple threads are allowed to perform read/write operations at a time.	Only one thread is allowed to perform read/write operations.
3.	Iterator is Fail-Safe.	Iterator is Fail-Fast.
4.	Never throw ConcurrentModificationException.	Possible to throw ConcurrentModification Exception.
5.	While iterating CopyOnWriteArrayList by iterator we cannot perform remove () operation.	While iterating Synchronized list by iterator we can perform remove () operation.

 

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    What the the new methods introduced in CopyOnWriteArrayList to performing read and write operation?

-          CopyOnWriteArrayList is is concurrent version of list implementation.

-          All methods of the list will be by default available in CopyOnWriteArrayList.

-          There are a couple of methods that have been introduced by CopyOnWriteArrayList.

1.       addIfAbsent():This method will add an element if and only if an element is not present in the list. Please refer to the below example.

package simplifiedjava.crackedInterview;  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.addIfAbsent(20);// This element will be ignored because its already in list.             list.addIfAbsent(40);// This element will be added because it was not in list.             System.out.println(list);                 } } Output: [10, 20, 30, 40]

 

2.       addAllAbsent(): This method will add all elements if and only if elements are not present in the list. Please refer to the below example.

package simplifiedjava.crackedInterview;  import java.util.concurrent.CopyOnWriteArrayList;  public class CopyOnWriteArrayListDemo {        public static void main(String[] args) {             CopyOnWriteArrayList<Integer> list1 = new CopyOnWriteArrayList<Integer>();             list1.add(10);             list1.add(20);             list1.add(30);             System.out.println("List 1 = "+ list1);                        CopyOnWriteArrayList<Integer> list2 = new CopyOnWriteArrayList<Integer>();             list2.add(10);             list2.add(20);             list2.add(40);             System.out.println("List 2 "+ list2);                        list1.addAllAbsent(list2);             System.out.println("Updated List = "+ list1);               } } Output: List 1 = [10, 20, 30] List 2 [10, 20, 40] Updated List = [10, 20, 30, 40]

 

    What is CopyOnWriteArraySet? How does it work internally?

-          It is a thread-safe version of Set.

-          Internally implemented with CopyOnWriteArrayList.

-          Insertion order is always preserved.

-          Duplicates are not allowed.

-          Null is allowed.

-          Multiple threads can perform read operation without lock but for every update, a clone copy will be created.

-          When one thread is iterating a set another thread is allowed to access the same resources still we won’t get ConcurrentModificationException.

-          You can’t perform the remove operation while traversing the set object using an iterator otherwise it will throw UnSupportedOperationException.

-          Iterator is Fail-safe.

 

    Can CopyOnWriteArraySet preserve insertion order?

-          Yes, CopyOnWriteArraySet preserves the insertion order. 

• 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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