Inheriting static variable from abstract class

Question

I have half a dozen classes which all extend the same abstract class. The abstract class has a static variable pointing to some JNI code that I only want to load once per in

Answer 1

I have a similar problem. Looks like Java can't isolate static members (attributes). I ended up adding an abstract method instead of the attribute:

public abstract class Abs {
    public void printX() {
        System.out.println("For " + this.getClass() + " x=" + getX());
    }

    protected abstract Integer getX();

}

public class A extends Abs {
    protected static Integer x = 1;

    @Override
    protected Integer getX() {
        return x;
    }

}

public class B extends Abs {
    protected static Integer x = 2;

    @Override
    protected Integer getX() {
        return x;
    }

}

public class test {

    public static void main(String args[]) {
        Abs a = new A();
        a.printX();
        Abs b = new B();
        b.printX();
        Abs c = new A();
        a.printX();
        b.printX();
        c.printX();

    }
}

Answer 2

You can approximate it, but you will need separate static variables for each subclass, to stop subclasses overwriting each others values. It's easiest to abstract this via a getter getFoo so that each subclass fetches the foo from the right place.

Something like this

abstract class Bar
{
   // you don't have to have this in the base class 
   // - you could leave out the variable and make
   // getFoo() abstract.
   static private String foo;

   String getFoo() {
     return foo;
   }

   public void printFoo() {
      System.out.print(getFoo());
   }
}

class Foo1 extends Bar
{
   static final String foo1;

   public String getFoo() {
      return foo1;  // return our foo1 value
   }

   public Foo1() {
      foo1 = "myfoo1";
   }
}


class Foo2 extends Foo1
{
   static final String foo2;

   public String getFoo() {
      return foo2;  // return our foo2 value
   }

   public Foo2() {
      foo2 = "myfoo2";
   }
}