1. Java Concurrency Utilities - java.util.concurrent
2. Java BlockingQueue
3. ArrayBlockingQueue
4. DelayQueue
5. LinkedBlockingQueue
6. PriorityBlockingQueue
7. SynchronousQueue
8. BlockingDeque
9. LinkedBlockingDeque
10. Java ConcurrentMap
11. ConcurrentNavigableMap
12. CountDownLatch
13. CyclicBarrier
14. Exchanger
15. Semaphore
16. Java ExecutorService
17. Java Callable
18. Java Future
19. ThreadPoolExecutor
20. ScheduledExecutorService
21. Java ForkJoinPool
22. Java Lock
23. ReadWriteLock
24. AtomicBoolean
25. AtomicInteger
26. AtomicLong
27. AtomicReference
28. AtomicStampedReference
29. AtomicIntegerArray
30. AtomicLongArray
31. AtomicReferenceArray

• ConcurrentMap Implementations
  • ConcurrentHashMap
• ConcurrentMap Example

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");