ConcurrentMap
Jakob Jenkov |
java.util.concurrent.ConcurrentMap
The java.util.concurrent.ConcurrentMap interface represents a Map
which is capable of handling concurrent access (puts and gets) to it.
The ConcurrentMap has a few extra atomic methods in addition to the methods it inherits from
its superinterface, java.util.Map.
ConcurrentMap Implementations
Since ConcurrentMap is an interface, you need to use one of its implementations
in order to use it. The java.util.concurrent package contains the following implementations
of the ConcurrentMap interface:
- ConcurrentHashMap
ConcurrentHashMap
The ConcurrentHashMap is very similar to the java.util.HashTable class, except
that ConcurrentHashMap offers better concurrency than HashTable does.
ConcurrentHashMap does not lock the Map while you are reading from it. Additionally,
ConcurrentHashMap does not lock the entire Map when writing to it. It only
locks the part of the Map that is being written to, internally.
Another difference is that ConcurrentHashMap does not throw ConcurrentModificationException
if the ConcurrentHashMap is changed while being iterated. The Iterator is not designed
to be used by more than one thread though.
Checkout the official JavaDoc for more details about ConcurrentMap and ConcurrentHashMap.
ConcurrentMap Example
Here is an example of how to use the ConcurrentMap interface. The example uses
a ConcurrentHashMap implementation:
ConcurrentMap concurrentMap = new ConcurrentHashMap();
concurrentMap.put("key", "value");
Object value = concurrentMap.get("key");
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