Singleton con subclasificación en Java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;

abstract class Singleton {

    private static Singleton instance;

    protected Singleton() {}

    public static Singleton getInstance() {
        if (instance == null) {
            String line = Singleton.getSingletonConfigure();
            try {
                instance = (Singleton)Class.forName("com.design_patterns.singleton." + line)
                                .getDeclaredConstructor().newInstance();
            } catch (InstantiationException | IllegalAccessException | IllegalArgumentException
                    | InvocationTargetException | NoSuchMethodException | SecurityException
                    | ClassNotFoundException e) {
                System.out.println("Falló la configuración.");
            }
        }
        return instance;
    }

    private static String getSingletonConfigure() {
        BufferedReader in = null;
        String className = "";
        try {
            in = new BufferedReader(new FileReader("singletonConfigure"));
            className = in.readLine();
        } catch (IOException ex) {
            System.out.println("IOException al leer: " + ex.getMessage());
        } finally {
            if (in != null) {
                try {
                    in.close();
                } catch (IOException ex) {
                    System.out.println("IOException al cerrar: "
                            + ex.getMessage());
                }
            }
        }
        return className;
    }

    protected abstract void showInstance();

}

class ASingleton extends Singleton {

    protected ASingleton() {
        super();
    }

    @Override
    protected void showInstance() {
        System.out.println("ASingleton");

    }

}

class BSingleton extends Singleton {

    protected BSingleton() {
        super();
    }

    @Override
    protected void showInstance() {
        System.out.println("BSingleton");

    }

}

class Client {

    private static void execute() {
        Singleton.getInstance().showInstance();
    }

    public static void main(String[] args) {
        execute();
    }

}