InetAddressClass

 package java.net;
InetAddress.class

 static Object loadImpl(String implName) {
	Object impl;

        /*
         * Property "impl.prefix" will be prepended to the classname
         * of the implementation object we instantiate, to which we
         * delegate the real work (like native methods).  This
         * property can vary across implementations of the java.
         * classes.  The default is an empty String "".
         */
        String prefix = (String)AccessController.doPrivileged(
                      new GetPropertyAction("impl.prefix", ""));
        impl = null;
        try {
            impl = Class.forName("java.net." + prefix + implName).newInstance();
        } catch (ClassNotFoundException e) {
            System.err.println("Class not found: java.net." + prefix +
                               implName + ":\ncheck impl.prefix property " +
                               "in your properties file.");
        } catch (InstantiationException e) {
            System.err.println("Could not instantiate: java.net." + prefix +
                               implName + ":\ncheck impl.prefix property " +
                               "in your properties file.");
        } catch (IllegalAccessException e) {
            System.err.println("Cannot access class: java.net." + prefix +
                               implName + ":\ncheck impl.prefix property " +
                               "in your properties file.");
        }

        if (impl == null) {
            try {
                impl = Class.forName(implName).newInstance();
            } catch (Exception e) {
                throw new Error("System property impl.prefix incorrect");
            }
        }

	return impl;
    }
}