HashMap is the Class which is under Traditional Collection and ConcurrentHashMap is a Class which is under Concurrent Collections, apart from this there are various differences between them which are:
- HashMap is non-Synchronized in nature i.e. HashMap is not Thread-safe whereas ConcurrentHashMap is Thread-safe in nature.
- HashMap performance is relatively high because it is non-synchronized in nature and any number of threads can perform simultaneously. But ConcurrentHashMap performance is low sometimes because sometimes Threads are required to wait on ConcurrentHashMap.
- While one thread is Iterating the HashMap object, if other thread try to add/modify the contents of Object then we will get Run-time exception saying ConcurrentModificationException.Whereas In ConcurrentHashMap we wont get any exception while performing any modification at the time of Iteration.
Using HashMap
Output:
100=A
Exception in thread "main" java.util.ConcurrentModificationException
Using ConcurrentHashMap
Output:
100=A
101=B
102=C
103=D
{100=A, 101=B, 102=C, 103=D}
In HashMap, null values are allowed for key and values, whereas in ConcurrentHashMap null value is not allowed for key and value, otherwise we will get Run-time exception saying NullPointerException.
Using HashMap
output:
{null=World, 100=Hello, 101=Geeks, 102=Geeks}
Using ConcurrentHashMap
