Interview questions on Concurrent Collections in java for experienced

 Part 2

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

    What is the difference between HashMap and ConcurrentHashMap?

	HashMap	ConcurrentHashMap
1.	HashMap is not thread-safe.	ConcurrentHashMap is thread-safe.
2.	Only one null key and multiple null values are allowed.	ConcurrentHashMap doesn’t allow null keys or values either. It will throw NullPointerException at runtime.
3.	The performance of HashMap is high as compared to ConcurentHashMap because multiple threads can access the same object.	The performance of ConcurrentHashMap is relatively low because it is thread-safe.
4.	Thread gets a lock of the whole object and then execute.	In ConcurrentHashMap thread won’t take whole objects lock, Thread will get Segment lock or bucket lock.
5.	If multiple threads are trying to perform write or read operations on the same collection object then we will get ConcurrentModifcationException.	Multiple threads are allowed to perform a read operation and 16 or more threads are allowed to perform the write operation.
6.	HashMap has only one lock available.	ConcurrentHashMap can have one or multiple locks we call it a Concurrency level.
7.	Iterator is Fail-Fast.	Iterator is Fail-Safe.
8.	When multiple threads access the same resource at a time then iterator fails immediately is called Fail-Fast.	When multiple threads access the same resources at a time, Iterator won’t fail is called Fail-Safe Iterator.

 

    What is the difference between HashTable and ConcurrentHashMap?

	HashTable	ConcurrentHashMap
1.	Thread will get whole object lock.	Thread will get a bucket level or Setment level lock instead of whole object lock.
2.	Only one thread is allowed to perform thread safe operation.	Multiple threads are allowed to perform thread-safe operation at a time.
3.	Every read and write operation require object level lock.	Read operation can perform without lock and write operation can perform by getting bucket level or Segment level lock.
4.	When one thread is performing read operation no other threads are allowed to perform any operation on same object otherwise you will get ConcurrentModificationException.	When one thread is performing read operation other threads are allowed to perform write operation on same object still you won’t get ConcurrentModificationException.
5.	Iterator is Fail-Fast	Iterator is Fail-Safe.
6.	Introduced in Java 1.0	Introduced in Java 1.5.

3.       

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    What is the difference between SynchronizedHashMap and ConcurrentHashMap?

	SynchronizedHashMap	ConcurrentHashMap
1.	The thread will get the whole object locked.	The thread will get a bucket level or Segment level lock instead of a whole object lock.
2.	Only one thread is allowed to perform the thread-safe operation.	Multiple threads are allowed to perform the thread-safe operation at a time.
3.	Every read and write operation require a full object lock.	Read operation can perform without lock and write operation can perform by getting bucket level or Segment level lock.
4.	When one thread is performing a read operation no other thread is allowed to perform any operation otherwise we will get ConcurrentModificationException.	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.
5.	Iterator is Fail-Fast.	Iterator is Fail-Safe.
6.	Introduced in Java 1.2	Introduced in Java 1.5.

 

• 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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