Static block in superclass to initialize static members in subclasses

Question

I am trying to create several classes that are all very similar and should derive from a super class because they all have common members and are all initialized the same way. I would prefer every member of my subclasses to be static and final as they will be initialized once and only once. I can not figure out the best way to make this work. Here is an example (using code that does not work, but you can see what I am trying to do):
class Super
    protected static final String initializedInEachSubclass;
    protected static final String alsoInitializedInEachSubclass;
    // these need to be accessed from anywhere
    public static final String initializedInSuperclass;
    public static final String alsoInitializedInSuperclass;
    // this static initialization block is exactly the same for every instance
    static
        // initialize these based on what the subclasses initialized
        initializedInSuperclass = initializedInEachSubclass + alsoInitializedInEachSubclass;
    private Super () {} // never instantiated
    public static final String getMoreInfo ()
        // the same for each instance
        return Integer.toString (initializedInEachSubclass.length ());
class Sub1 extends Super
    static
        initializedInEachSubclass = "My String for Sub1";
        alsoInitializedInEachSubclass = "My Other String for Sub1";
    private Sub1 () {} // never instantiated
}The problem with the above code is that the static block in Super uses static final variables that have not been initialized yet. I can't make Super abstract. If I initialize the final variables in Super, then I can not reinitialize them in Sub1. But if they are not final, then they could be changed after being initialized (which I would rather not allow). I could make everything protected and not final and then make public get... () methods, but I like accessing them as attributes. It seems like this should be possible, but everything I have tried has led me to a catch-22.
Any ideas on how I can put all my redundant initialization code in one place but still allow the subclasses to initialize the static members that make each of them unique? I will be happy to clarify my examples if you need more information.
Edited by: sawatdee on Jan 3, 2008 9:04 AM

Answer 1

sawatdee wrote:
I am basically trying to avoid having redundant code in several classes when the code will be exactly the same in all of them.That's the wrong reason to subclass. You subclass to express type specialization. That is, a Dog IS-A Mammal, but it's a special type of Mammal that implements certain common mammal behaviors in a dog-specific way. A LinkedList IS-A List, but in implements common list operations in linked-list-specific ways.
I don't really need to have the static final members in a superclass (and I don't even need a superclass at all), but I don't know how else to execute a big static initialization block in several classes when that code is exactly the same in all of them. Without knowing more details about what you're trying to do, this sounds like a case for composition rather than inheritance. What's now your superclass would be a separate class that all your "sublasses" have a reference to. If they each need their own values for its attributes, they'd each have their own instances, and the stuff that's static in the current superclass would be non-static in the "subs". If the values for the common attributes are class-wide across the "subs", the contained former super can be static.
public class CommonAttrs {
  private final String attr1;
  private final int attr2;
  public CommonAttrs(String attr1, int attr2) {
    this.attr1 = attr1;
    this.attr2 = attr2;
public class FormerSub1 {
  private static final CommonAttrs = new CommonAttrs("abc", 123);
... etc. ..