LibrarySL.java

class ServiceLocator...
    private static ServiceLocator sInstance;
    public static void load(ServiceLocator arg) {
        sInstance = arg;
    }
    private Map services = new HashMap();
    public static Object getService(String key){
        return sInstance.services.get(key);
    }
    public void loadService (String key, Object service) {
        services.put(key, service);
    }
   .....
   .....
}

// A simple assembler class.
class Tester {
   private void configure() {
        ServiceLocator locator = new ServiceLocator();
        locator.loadService("LocalBookFinder", new LocalBookFinder());
        locator.loadService("RemoteBookFinder", new RemoteBookFinder());      
        ServiceLocator.load(locator);
    }
}

class Library...
BookFinder finder = (BookFinder) ServiceLocator.getService("LocalBookFinder");