Concurrent collections in java

If you are a beginner then read the collection framework and then move further. Because this post is directly related to collections of java. We have discussed all the collection classes and interface in recent posts.
Concurrent collections in java are designed and optimized specifically for synchronized multithreaded access. These are the thread safe collections, and these are existing in java.util.concurrent package. In this post, we will see all the java concurrent collections and find see how to use thread safe collections java.

Concurrent collections in java

Need of Concurrent Collections

As we know Java supports multithreading and concurrency, we achieve the synchronization by use of the synchronization keyword. The collection framework provides various collections and we can make them thread-safe by use of the synchronized keyword. But there are some problems that occur when we use the Collections concept in multi-threading without the synchronized keyword.

1. In the Collection framework most of the Collection classes are not thread-safe because those are non-synchronized. Like ArrayListLinkedListHashMap is non-synchronized in nature. If multiple threads will perform any operation on an object simultaneously. Then the data will not be in proper synchronized and leads to data redundancy

2. We can’t modify the collection while iterating the Collection object. If we try to modify the collection, it throws ConcurrentModificationException. So non-synchronized collections are not good choice for Multi-threaded applications.

To overcome these problems Java introduced a new feature in JDK 1.5 Version. It introduced some thread safe collections java.

Concurrent collections in java
Java concurrent collections were introduced in version 5 and part of the java.util.concurrent package. Here java introduced some more classes that are designed for concurrent access from multiple threads.

For example, HashMap is non-synchronized class but ConcurrentHashMap class is synchronized hash-based Map implementation.

Here we have some java Concurrent collection classes:
1. Immutable List in Java
2. CopyOnWriteArrayList in java
3. Immutable Set in Java
4. CopyOnWriteArraySet in java
5. ConcurrentHashMap in java

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