How to create a function that cannot be executed by a constructor?

Say I have function x which is a function in an abstract class. x adds itself to a private arraylist if it does not already contain it. I want to make a function that cannot be executed inside the constructor so that 'x' cannot be added to the arraylist if the constructor errors, and can only be called after the constructor(s) has finished. The gist of my situation is that I want the set to be private so only the class A can access it, nothing should ever be removed from the list if it is added, the addToArray function should only ever need to happen once and should never happen from the constructor. The constructor would only matter if it is a subclass' constructor.

public abstract class A {
    public A () {
        //do stuff :)
    }
    public abstract void doStuff();
    public final void addToArray() {
        if(isCalledFromConstructor/*HELP ME HERE*/)
            throw new RuntimeException("Cannot execute addToArray function from a constructor");
        if(!AS.contains(this))AS.add(this);
    }
    private static final java.util.Set<A> AS = new java.util.concurrent.ConcurrentSkipListSet<A>();
    public static final class B extends A {
        public B(){
            addToArray();//THROW AN ERROR HERE
        }
        @Override
        public void doStuff(){
            System.out.println("Doing stuff");
        }
    }
}

With more context on what you’re trying to accomplish, I might be able to give a better suggestion on achieving your ultimate goal. That said, if you are absolutely set on doing what you are asking, one way is to call

Thread.currentThread().getStackTrace()

from within addToArray and examine the contents of the stack trace to see if you’re currently inside of a constructor.

In particular this

  boolean isCalledFromConstructor() {
    StackTraceElement[] stackTrace = Thread.currentThread().getStackTrace();
    for (StackTraceElement stackTraceElement : stackTrace) {
      String methodName = stackTraceElement.getMethodName();
      if (methodName.equals("<init>")) return true;
    }
    return false;
  }

should do it for you, although it's not my favorite bit of code

As other people have commented, doing this may be a sign of a design oversight. Please give more details on the big picture goal if you can.

You could have a private variable like boolean isInitialized and set this to true in constructor. In the add method check if this value is false and throw error.

If your environment allows it you could use @PostConstruct method annotation to add it to your list safely.

But i also recommend to check your code design. You are adding an instance to a private static list that is not thread safe.