Superclass Constructor calling overridable validation method

Question

I have the following class:
public class SuperClass
   private int x;
   public SuperClass(int x)
      setX(x);
   protected void validateX(int x)
      if(x < 0)
         throw new IllegalArgumentException("x < 0");
   public int getX()
      return x;
   public void setX(int x)
      validateX(x);
      this.x = x;
}My question is: How can I avoid calling setX(int) in the constructor besides simply dupicating validateX(int) in the constructor if I want to subclass SuperClass? [I read in a recent Java Fundamentals newsletter that calling overridable methods in superclass constructors is a bad idea int that it tends to destabilize the whole class hierarchy.  I don't want to make validateX(int) and setX(int) final.]

Answer 1

Never call overrideable methods from constructors. No exceptions.
You can use a factory method to validate your object after its created if you must.
public class SuperClass
   private int x;
   public SuperClass()
   static SuperClass createSuperClass(int x){
         SuperClass sc = new SuperClass();
         sc.setX(x);
         return sc;
   protected void validateX(int x)
      if(x < 0)
         throw new IllegalArgumentException("x < 0");
   public int getX()
      return x;
   public void setX(int x)
      validateX(x);
      this.x = x;
}Or you can use template method
public class SuperClass
private int x;
public SuperClass(int x)
setXImpl(x);
final protected void validateX(int x)
if(x < 0)
throw new IllegalArgumentException("x < 0");
public int getX()
return x;
final void setXImpl(int x){
validateX(x);
this.x = x;
public void setX(int x)
setXImpl(x);
In general I don't like to call any overrideable methods from within my class. I try not to be anal about it though. My personal choice would be to duplicate the set method in the constructor. You should be constructing the object not using it. access instance variables not methods.