ConcurrentHashMap in Java is introduced as an alternative of
Hashtable in Java 1.5 as part of Java concurrency package. Prior
to Java 1.5 if you need a Map implementation, which can be
safely used in a concurrent and multi-threaded Java program,
than, you only have Hashtable or synchronized Map because
HashMap is not thread-safe. With ConcurrentHashMap, now you have
better choice; because, not only it can be safely used in
concurrent multi-threaded environment but also provides better
performance over Hashtable and synchronizedMap.
ConcurrentHashMap performs better than earlier two because it
only locks a portion of Map, instead of whole Map, which is the
case with Hashtable and synchronized Map. CHM allows concurred
read operations and same time, maintains integrity by
synchronizing write operations. We have seen basics of
ConcurrentHashMap on Top 5 Java Concurrent Collections from JDK
5 and 6 and in this Java tutorial, we will learn : Ø How
ConcurrentHashMap works in Java or how it is implemented in
Java. Ø