volatile

volatile guarantees that every write is immediately visible to all threads (visibility), but it does not make compound operations like counter++ atomic.

volatile fails for compound actions (counter++), check-then-act (if-then-modify), and multi-variable invariants because it guarantees visibility of individual reads and writes but not atomicity of compound operations.

No: volatile alone cannot guarantee thread safety for a counter because counter++ is three operations, and two threads can read the same value before either writes back.

volatile provides visibility only (for flags and status), while Atomic classes provide visibility plus atomicity via hardware CAS (for counters and conditional updates).

Without volatile, the JIT compiler can hoist a flag read out of a loop, caching it in a CPU register, so the loop never sees updates from another thread and runs forever.