java - Iterate / recurse through Containers and Components to find objects of a given class?

Question

I've written a MnemonicsBuilder class for JLabels and AbstractButtons. I would like to write a convenience method setMnemonics( JFrame f ) that will iterate through every child of the JFrame and select out the JLabels and AbstractButtons. How can I obtain access to everything contained in the JFrame? I've tried:

LinkedList<JLabel> harvestJLabels( Container c, LinkedList<JLabel> l ) {
    Component[] components = c.getComponents();
    for( Component com : components )
    {
        if( com instanceof JLabel )
        {
            l.add( (JLabel) com );
        } else if( com instanceof Container )
        {
            l.addAll( harvestJLabels( (Container) com, l ) );
        }
    }
    return l;
}

In some situations, this works just fine. In others, it runs out of memory. What am I not thinking of? Is there a better way to search for child components? Is my recursion flawed? Is this not a picture of how things "Contain" other things in Swing - e.g., is Swing not a Rooted Tree?

JFrame
|
|\__JMenuBar
|   |
|    \__JMenu
|       |
|        \__JMenuItem
|
|\__JPanel
|   |
|   |\__JButton 
|   |
|   |\__JLabel
|   |
|   |\__ ... JCheckBoxes, other AbstractButtons, etc.

Answer 1

Agree with Tom here... Your problem is that you're already passing the List to add the JLabels down to your recursive method AND you're also returning it - thus adding the same items to your list more than once. In more politically correct terms - the List is your accumulator.

Your method should instead look like this:

public void harvestJLabels(Container c, List<JLabel> l) {
    Component[] components = c.getComponents();
    for(Component com : components) {
        if(com instanceof JLabel) {
            l.add((JLabel) com);
        } else if(com instanceof Container) {
            harvestJLabels((Container) com, l));
        }
    }
}

Then you can have a helper method to initiate this harvesting:

public List<JLabel> harvestJLabels(Container c) {
    List<JLabel> jLabels = new ArrayList<JLabel>();
    harvestJLabels(c, jLabels);
    return jLabels;
}