code: @Override
  	public synchronized void initialize(Manager manager) {
  		if (this.manager != null) {
  			throw new IllegalStateException("Callback was already initialized");
  		}
  		this.manager = manager;
  		for (Callback callback : callbacks) {
  			try {
  				callback.initialize(manager);
  			} catch (Exception e) {
  				onManagerWarning("Callback initialization error", e);
  			}
  		}
  	}
docs: Calls initialize on all children.