What are the key differences between volatile variables and atomic data types?

Variables marked with volatile guarantee that reading and writing to this variable will occur directly from main memory, not from the processor cache. This ensures visibility of changes to the variable between threads, but does not guarantee the atomicity of operations. That is, operations like increment (x++) are not atomic and can lead to race conditions.

Atomic data types (for example, AtomicInteger in Java) provide methods that are executed atomically — without interruptions and with guarantees of correctness in concurrent access. They ensure both visibility and atomicity of operations, allowing safe modification of the variable's value from multiple threads without using locks.

Example in Java:

volatile int counter = 0; // visibility of changes, but not atomicity
AtomicInteger atomicCounter = new AtomicInteger(0); // atomic operations

// Incorrect for volatile:
counter++;

// Correct for AtomicInteger:
atomicCounter.incrementAndGet();