What is the difference between using the 'volatile' keyword for atomic operations and synchronized blocks in Java?

The volatile keyword in Java guarantees visibility of changes to a variable between threads, meaning when one thread modifies the value of a volatile variable, other threads will immediately see this change. However, volatile does not ensure atomicity of complex operations (e.g., increment), only read and write of primitive types.

Synchronized blocks (synchronized) provide both visibility and atomicity: they lock access to code or data, allowing only one thread to execute the critical section at a time. This prevents race conditions when modifying shared data.

Example:

volatile int counter = 0;

// Increment is not atomic, even with volatile
counter++;

// Synchronization for atomic increment
synchronized(this) {
    counter++;
}

In summary:

• volatile guarantees freshness of the value but not atomicity of operations.
• synchronized guarantees both atomicity and visibility, but with overhead due to locking.