The Atomic classes in Java 5

In our outline of how synchronization works, we saw that under the hood, a machine instruction generally called Compare-And-Swap (CAS) was used to effectively read and write to a memory location at the same time. From Java 5 onwards, CAS and related instructions are effectively exposed at the level of the Java programmer in the form of a series of "atomic" classes in the java.util.concurrent package:

• Classes providing atomic access to main primitive types or to an object reference: AtomicBoolean, AtomicInteger and AtomicLong, AtomicReference;
• Classes providing atomic access to fields in arrays of the correspoding types: AtomicIntegerArray, AtomicLongArray, AtomicReferenceArray;
• Classes to atomically couple a boolean or integer with a reference field: AtomicMarkableReference and AtomicStampedReference;
• Atomic field updaters: classes to wrap up atomic access, via reflection, to volatile fields of another class (AtomicIntegerFieldUpdater, AtomicLongFieldUpdater and AtomicReferenceFieldUpdater);
• Concurrent collection classes, including significantly a highly concurrent hash map implementation.

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