Question

I am developing a swing app, where I have a Factory class which provide Component keeping Singleton in mind. Like:

public final class ComponentFactory {
    private static LibraryFrame libraryFrame;
    private static LibraryTableScrollPane libraryTableScrollPane;

    public static synchronized LibraryFrame getLibraryFrame() {
        if (libraryFrame == null) {
            libraryFrame = new LibraryFrame();
        }
        return libraryFrame;
    }

    public static synchronized LibraryTableScrollPane getLibraryTableScrollPane() {     
        if(libraryTableScrollPane == null) {
            libraryTableScrollPane = new LibraryTableScrollPane(getLibraryTable());
        }       
        return libraryTableScrollPane;
    }
}

I am using this component as:

add(ComponentFactory.getLibraryTableScrollPane())

Also I make a ListenerFactory class which provides various Listeners of Swing/AWT.

Is this pattern has any flaws? Can I use a same component or listener with two concurrently visible parent component?

Thanks in advance.

Answer 1

It has a major flaw: it promotes a lack of encapsulation by making every component globally accessible. This can lead very quickly to spaghetti code where every object uses any other object, instead of having a short list of dependencies providing encapsulated methods.

Another problem is with the implementation: the synchronization is unnecessary, since Swing components are not thread-safe, and may only be used from the event dispatch thread. You should thus only have the EDT calling your methods, which makes synchronization unnecessary.

Finally, a component may only have one parent component. If the same compoentnmust be displayed in two different frames, for example, you’ll need two instances of this component.