In Java Currency API, what are atomic classes?

In Java’s java.util.concurrent package, atomic classes are a set of classes that provide atomic operations on single variables without the need for external synchronization. These classes are designed to be used in concurrent and multi-threaded applications, where multiple threads may be accessing and modifying the same variable simultaneously.

The atomic classes in Java include:

1. AtomicBoolean: Provides atomic operations on a boolean variable.
2. AtomicInteger: Provides atomic operations on an integer variable.
3. AtomicLong: Provides atomic operations on a long variable.
4. AtomicReference: Provides atomic operations on a reference variable.
5. AtomicIntegerArray: Provides atomic operations on an array of integers.
6. AtomicLongArray: Provides atomic operations on an array of longs.
7. AtomicReferenceArray: Provides atomic operations on an array of references.

These atomic classes provide methods such as get, set, compareAndSet, getAndSet, incrementAndGet, and decrementAndGet that can be used to perform atomic operations on the underlying variable. These methods are designed to be thread-safe and guarantee that the operations will be performed atomically, without the need for external synchronization.

Atomic classes can be used to implement lock-free algorithms and data structures, and can be more efficient than using external synchronization mechanisms such as locks or synchronized blocks. However, they should be used with caution, as incorrect usage can lead to issues such as race conditions and data inconsistencies.