Java abstract class inheritance question

Question

I have an abstract class with a single concrete method. In this method I want to use a static class variable from the classes that derive from the one the method is declared in. To do so, I of course have to declare this static variable in the abstract class as well.

When the method is called, the variable is resolved to the one in my abstract base class as opposed to the one in the derived class. Do I need to decorate the derived class' property with an attribute?

Am I trying to do something that is not supported in Java, or am I just missing something?

Answer 1

You're trying to do something that isn't supported. Fields can't be "overridden" - and static members don't behave polymorphically.

Instead, create abstract properties which can be implemented in the derived classes. They'll have to be instance properties even if they return static variables.

Answer 2

Depending on what you want to do, you can do:

    Base b = new Sub();
    System.out.println(b.myInt); // will print myInt from Base

    Sub s = new Sub();
    System.out.println(s.myInt); // will print myInt from Sub

, but you likely want Jon's approach.

Answer 3

You can't override variables, only methods. If its likely that a subclass needs to give a different value, add a getter method to the class that does that.

abstract class Foo {
  static private final String someValue = "blah";

  String getSomeValue() {
    return someValue;
  }

  public abstract void someMethod();
}

class Bar extends Foo {
  String getSomeValue() {
    return "somethingElse";
  }

  public void someMethod() {
    String x = getSomeValue();
  }
}