In Java, why can't I declare a final member (w/o initializing it) in the parent class and set its value in the subclass? How can I work around?

Question

In a Java program, I have multiple subclasses inheriting from a parent (which is abstract). I wanted to express that every child should have a member that is set once only (

Answer 1

Why not delegate initialization to a method. Then override the method in the parent class.

public class Parent {
   public final Object x = getValueOfX();
   public Object getValueOfX() {
      return y;
   }
}
public class Child {
  @Override
  public Object getValueOfX() {
     // whatever ...
  }
}

This should allow custom initialization.