Java.Multithreading.In Counter class we dont use compareAndSet method, so how it works ?

we use smth like this in Counter class

AtomicInteger counter = new AtomicInteger(0);
counter.incrementAndGet();

👉 We don’t directly call compareAndSet() — but under the hood, incrementAndGet() uses compareAndSet() (or CAS instructions) internally!

🧠 Let’s Unpack It

Here’s what actually happens inside AtomicInteger.incrementAndGet():

public final int incrementAndGet() {
    return unsafe.getAndAddInt(this, valueOffset, 1) + 1;
}

And getAndAddInt() is implemented like this in the Unsafe class (simplified logic):

public final int getAndAddInt(Object obj, long offset, int delta) {
    int prev, next;
    do {
        prev = getIntVolatile(obj, offset);
        next = prev + delta;
    } while (!compareAndSwapInt(obj, offset, prev, next));
    return prev;
}

🔁 What’s Going On Here:

1. Get the current value (prev)
2. Compute new value (next = prev + delta)
3. Try to compareAndSwap from prev to next
4. If another thread changed it in the meantime → try again (loop)

🎯 So You’re Right:

You don’t see CAS in your own code when you use methods like:

• incrementAndGet()
• decrementAndGet()
• addAndGet()

But the JVM calls compareAndSwap inside those methods to ensure atomicity.

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🤖 CAS vs Synchronized Revisited

Operation	Under the hood	Locking?
synchronized block	JVM monitor/lock	✅ Yes
AtomicInteger.incrementAndGet()	CAS via Unsafe or VarHandle	❌ No