Need of synchronization in getters and setters

Question

Probably a very silly question. Just wanted to confirm my understanding.

class Test
{
       private volatile String id;

       public void setID(String id)
       {
             this.id = id;
       }

       public String getID()
       {
             return id;
       }
}

Lets say that an object of above class can be accessed by multiple threads. My understanding is that in case of simple getter and setters like above (doing simple initialization), I do not need to make these methods synchronized, correct ?
I guess volatile is needed as otherwise value of id can be outdated otherwise in different threads.
So, can anyone see any problem if we do not have these methods as synchronized ?

Answer 1

My understanding is that in case of simple getter and setters like above (doing simple initialization), I do not need to make these methods synchronized, correct ?

Correct, because what they get and set (an object reference) is treated atomically by the JVM.

The answer would be "No, you do need synchronization" if you were using a long or double and you didn't have it marked volatile.

Both aspects of this are covered in the JLS, §17.7:

17.7. Non-atomic Treatment of double and long

For the purposes of the Java programming language memory model, a single write to a non-volatile long or double value is treated as two separate writes: one to each 32-bit half. This can result in a situation where a thread sees the first 32 bits of a 64-bit value from one write, and the second 32 bits from another write.

Writes and reads of volatile long and double values are always atomic.

Writes to and reads of references are always atomic, regardless of whether they are implemented as 32-bit or 64-bit values.