Get subclass back when stored as superclass

So I've been trying to fix this for a few hours now, to no avail.

Basically, I have class A, and class B which extends A. A has a string field "name", and another field "id", class B changes name when instantiated. B is then later stored as A, and the only thing identifying that A class to the B class is the "id" field.

I need a way to get the changed "name" that the B class has, from the A class.

Here's a code example:

class A {
	public String name = "test";
	public String id = "A_ID";
	
	public A(String id) {
		if (id.equals("B_ID") {
			// how would I get the name field of the B class, without instantiating B
		}
	}
}
class B extends A {
	{
		name = "test1";
		id = "B_ID";
	}
}

And here's what I've tried:

class A {
	public static Map<String, Class<? extends A>> REGISTRY = new HashMap<>();
	
	public String name = "test";
    public String id = "A_ID"; // is B_ID when changed
	
	public Object getField(String key) {
		Field field = REGISTRY.get(this.id).getSuperclass().getDeclaredField(key);
        return field.get(this); // <- the issue
	}
}
class B extends A {
	static {
		REGISTRY.put("B_ID", B.class);
	}
    public B() {
		name = "test1";
        id = "B_ID";
    }

}

Here's the problem with my solution, passing this to field.get(this) returns the fields of the current A object, which is what we already have. I need the fields that B changes when instantiated, but when B gets instantiated it calls getField a few times, which then causes a perpetual loop, I need a way to get the fields from B without instantiating B.

I've tried casting A to B but that causes a ClassCastException.

Sorry that this is confusing, I can't send the entire class as it's literally 1k+ lines, but basically the ID field is the only data stored with A that remains from B, and I need a way to get the fields from B without instantiating it

EDIT: I think my example was confusing, here's an example of how pkm's answer still presents the issue.

import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;

class A {
    public static Map<String, Class<? extends A>> REGISTRY = new HashMap<>();

    public String name = "test";
    public String id; // is B_ID when changed

    public A(String id) {
        this.id = id;
        this.getField("name") // should output test1
    }

    public Object getField(String key) throws NoSuchFieldException, SecurityException,
            IllegalArgumentException, IllegalAccessException {
        Field field = REGISTRY.get(this.id).getSuperclass().getDeclaredField(key);
        return field.get(this); // <- the issue, still returns "test"
    }
}


class B extends A {
    static {
        REGISTRY.put("B_ID", B.class);
    }

    public B() {
        super("B_ID");
        name = "test1";
    }
}

public class main {

    public static void main(String[] args) throws NoSuchFieldException, SecurityException,
            IllegalArgumentException, IllegalAccessException {
        new B(); // To update the registry
        A a = new A("B_ID");
        System.out.println(a.id);                //--> output: B_ID
        System.out.println(a.getField("name"));      //--> output: test, should be test1
    }

}

Here is the corrected code:

import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;

class A {
  public static Map<String, Class<? extends A>> REGISTRY = new HashMap<>();

  public String name = "test";
  public String id = "A_ID"; // is B_ID when changed

  public Object getField(String key) throws NoSuchFieldException, SecurityException,
      IllegalArgumentException, IllegalAccessException {
    Field field = REGISTRY.get(this.id).getSuperclass().getDeclaredField(key);
    return field.get(this); // <- the issue
  }
}


class B extends A {
  static {
    REGISTRY.put("B_ID", B.class);
  }

  public B() {
    name = "test1";
    id = "B_ID";
  }

}


public class Test {
  public static void main(String[] args) throws NoSuchFieldException, SecurityException,
      IllegalArgumentException, IllegalAccessException {
    A a = new B();
    System.out.println(a.name);                //--> output: test1
    System.out.println(a.getField("id"));      //--> output: B_ID
  }
}

As per your statement: I need a way to get the changed "name" that the B class has, from the A class. It'a achieved correctly, B_ID.

Fixed this by changing the registry from Class<? extends A> to just A, and then registering a new instance of B. I think it might lead to issues down the road and I was avoiding doing this but it works for now.