Java multithreading ConcurrentModificationException

Question

I have several tests that run in parallel, and uses the method below. Please see the code below it throws ConcurrentModificationException occasionally. I cannot figure out how it can happen?

private static MyObject myObject; 

public void setupMyObject{
    syncronized(this){
       myObject = Optional.ofNullable(myObject).orElse(SomeConfig.ofDefaults());
    }
}

Answer 1

myObject is a static variable, to lock it you need to put class object in synchronized. Your present implementation doesn't lock it properly.

import java.util.Optional;

public class Test {

    private static String myObject;

    public void setupMyObject(){
        synchronized(Test.class){
            myObject = Optional.ofNullable(myObject).orElse(SomeConfig.ofDefaults());
        }
    }

}