Is iinc atomic in Java?

Question

I know increment operation is not atomic in C++ without locking.

Will JVM add any lock on its implementation of iinc instruction?

Answer 1

No its not

• Retrieve the current value of c.
• Increment the retrieved value by 1.
• Store the incremented value back in c.

Java Documentation for Atomicity and Thread Interference

You need to either use synchronized keyword or use AtomicXXX methods for Thread safety.

UPDATE:

public synchronized void increment() {
    c++;
}

or

AtomicInteger integer = new AtomicInteger(1);
//somewhere else in code
integer.incrementAndGet();

Also read: Is iinc atomic in Java?