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copied!<p>On the java.util.concurrent package <a href="http://download.oracle.com/javase/6/docs/api/java/util/concurrent/package-summary.html#MemoryVisibility" rel="nofollow noreferrer">Memory Consistency Properties</a>, you can check the Javadoc API for the package:</p> <blockquote> <p>The methods of all classes in java.util.concurrent and its subpackages extend these guarantees to higher-level synchronization. In particular: </p> <ul> <li>Actions in a thread prior to placing an object into any concurrent collection <em>happen-before</em> actions subsequent to the access or removal of that element from the collection in another thread.<br> [...]</li> <li>Actions prior to "releasing" synchronizer methods such as<br> Lock.unlock, Semaphore.release, and<br> CountDownLatch.countDown<br> <em>happen-before</em> actions subsequent to a successful "acquiring" method such as Lock.lock, Semaphore.acquire, Condition.await, and CountDownLatch.await on the same synchronizer object in another thread.<br> [...]</li> </ul> </blockquote> <p>So, the classes in this package make sure of the concurrency, making use of a set of classes for thread control (<a href="http://download.oracle.com/javase/6/docs/api/java/util/concurrent/locks/Lock.html" rel="nofollow noreferrer"><code>Lock</code></a>, <a href="http://download.oracle.com/javase/6/docs/api/java/util/concurrent/Semaphore.html" rel="nofollow noreferrer"><code>Semaphore</code></a>, etc.). This classes handle the <em>happen-before</em> logic programmatically, i.e. managing a FIFO stack of concurrent threads, locking and releasing current and subsequent threads (i.e. using <code>Thread.wait()</code> and <code>Thread.resume()</code>, etc.</p> <p>Then, (theoretically) you don't need to synchronize your statements accessing this classes, because they are controlling concurrent threads access programmatically.</p>

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