In this article, we will discuss difference between CopyOnWriteArraySet and HashSet classes in detail i.e.; CopyOnWriteArraySet v/s HashSet
Lets us move on and discuss key differences between these 2 Set classes
1. CopyOnWriteArraySet v/s HashSet :
- COWAL –> CopyOnWriteArrayList
- COWAS –> CopyOnWriteArraySet
| CopyOnWriteArraySet | HashSet |
| CopyOnWriteArraySet is synchronized and it is internally implemented using COWAL | HashSet is not synchronized |
| For every update operation, a new separate cloned copy is created and there is memory & merging overhead for JVM
Hence, performance is relatively low when comparing with HashSet | In multi-threaded environment, HashSet is faster than CopyOnWriteArraySet as multiple threads can operate
Hence, performance is high as there is no need to acquire lock |
| While one thread iterating CopyOnWriteArraySet items, other threads happily can modify, as it works on separate cloned copy
And it never throws ConcurrentModificationException | While one thread iterating HashSet items, if any other thread tries to modify same HashSet object then ConcurrentModificationException is thrown |
| That’s it is fail-safe iterator | That’s it is fail-fast iterator |
| Iterator of CopyOnWriteArraySet can perform read operation safely; while iterating through COWAS items
But as soon as, remove operation is performed, compiler throws UnsupportedOperationException | Iterator of HashSet can perform both read and remove operations; while iterating through HashSet elements |
| Present in java.util.concurrent package and qualified class name is java.util.concurrent .CopyOnWriteArraySet | Present in java.util package and qualified class name is java.util.HashSet |
| This is introduced in Java 1.5 version | This is introduced in original collection framework in Java 1.2 version |
Q) When to use HashSet ?
- HashSet stores unique elements using hashing technique
- So, search operation is faster
- So, if business requirement is to store unique elements for faster search operation or more number of search operation without concerning insertion order
- Then, HashSet is the very apt choice
Q) When to use CopyOnWriteArraySet ?
- This is the best suit to store unique elements as per insertion order in a multi-threaded environment
- Where there are more number of read operation and very less update/modify operation
- Because for every update/modify operations, a new separate cloned copy is created
- And there is overhead on JVM to allocate memory & merging cloned copy with original copy
- The advantage of using CopyOnWriteArraySet over HashSet is that, it doesn’t throws ConcurrentModificationException when multiple threads performs operation simultaneously
2. CopyOnWriteArraySet v/s HashSet :
- there is always a catch between performance and thread-safety
- choose wisely for your requirement
Related Articles:
- Java 5 – Introduction to Concurrent Collection
- Java 5 – CopyOnWriteArraySet class with example
- Java 5 – CopyOnWriteArraySet v/s HashSet
- Java 5 – CopyOnWriteArrayList v/s SynchronizedList
- Java 5 – Concurrent Collection Interview question and answers
References:
- https://docs.oracle.com/javase/tutorial/collections/intro/
- https://docs.oracle.com/javase/tutorial/collections/interfaces/collection.html
- https://docs.oracle.com/javase/7/docs/api/java/util/Collection.html
- https://docs.oracle.com/javase/tutorial/essential/concurrency/collections.html
- https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/CopyOnWriteArrayList.html
- https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/CopyOnWriteArraySet.html
- https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/CopyOnWriteArraySet.html
Happy Coding !!
Happy Learning !!