AtomicBoolean vs Synchronized block, whats the difference

Question

I am trying to understand the difference between the two following code blocks

AtomicBoolean ab = new AtomicBoolean(false);  

using the following to get and set state. .
ab.get();
ab.set(X);

vs. 

private boolean ab = false;
private final Object myboollock = new Ojbect();

public void setAB(boolean state)
{
    synchronized(myboollock)
     {
          ab = state;
     }
}

public boolean getAB()
{
 synchronized(myboollock)
 {
         return ab;
 }
}

I need to thread protect a boolean, that is all, and have in the past used the later method, but would like to start to use Atomic objects, (if ) they are safe?,

Evening

How about... reading the javadoc of AtomicBoolean? It describes the guarantees offered and the advantages over synchronization. – Gonsalve

please point me to the java doc that explains "clearly" the advantages of one over the other. I can't find it in docs.oracle.com/javase/8/docs/api/java/util/concurrent/atomic/… – Evening

Look at the javadoc for the package java.util.concurrent.atomic : docs.oracle.com/javase/8/docs/api/java/util/concurrent/atomic/… – Marianamariand

Answer 1

There are a few subtle differences but seen from the outside the two code snippets behave similarly: if you call the set method, the change will be visible to other threads calling get subsequently.

The main differences are:

• performance: depending on the level of contention, you may get better performance with synchronized or AtomicBoolean
• atomicity: if at some stage you want to do more than just setting the boolean value, a synchronized block will allow you to add instructions atomically but AtomicBoolean won't

Tramway

Answer 2

If all you're trying to do is make getting and setting a single boolean value atomic, then yes - you can use AtomicBoolean instead without any synchronization.

Of course, synchronized allows a far wider range of uses, such as performing several actions within the block without losing the lock, or using it for wait/notify. So it's not like AtomicBoolean is a general alternative to synchronization - but in this case you can use it instead of synchronization.

Connacht