Java: The Volatile Keyword

It ensures that a variable's value is always read from and written to main memory.

The 'volatile' keyword in Java is used to ensure that a variable is visible to all threads. When a variable is declared volatile, it means that any read or write of that variable will go directly to main memory, bypassing the CPU cache. This ensures that changes made by one thread are immediately visible to other threads. However, it does not ensure atomicity of compound operations like incrementing a counter.