public void registerUpdateListener(Consumer<PropertiesAssistant> listener) {
        if (listener != null)
            listeners.add(new WeakReference<>(listener));
    }
public void registerUpdateListener(Consumer<PropertiesAssistant> listener) {
        if (listener != null)
            listeners.add(new WeakReference<>(listener));
    }
public void registerUpdateListener ( Consumer < PropertiesAssistant > listener ) { if ( listener != null ) listeners . add ( new WeakReference <> ( listener ) ) ; }
the listener will always be called, when the Properties-file changes.

@param listener the listener
the listener will always be called when the Properties - file changes .