What will happen to the result if multiple threads simultaneously try to increment a variable declared as volatile?

A variable declared as volatile guarantees visibility of changes between threads, meaning each thread will see the current value of the variable. However, an increment operation (for example, volatileVar++) is not atomic — it consists of three steps: reading the value, incrementing, and writing back.

If multiple threads perform an increment on a volatile variable simultaneously, updates may be lost due to race conditions. As a result, the final value may be less than expected.

To correctly increment, you should use atomic classes from java.util.concurrent.atomic, such as AtomicInteger:

import java.util.concurrent.atomic.AtomicInteger;

AtomicInteger counter = new AtomicInteger(0);

// In threads
counter.incrementAndGet();

Thus, volatile only provides visibility, not atomicity of operations.