This sample shows the entire Codename One FileSystemStorage hierachy as a tree that can be expaneded

FileSystemStorageTreeSample.java

Form hi = new Form("FileSystemTree", new BorderLayout());
TreeModel tm = new TreeModel() {
    @Override
    public Vector getChildren(Object parent) {
        String[] files;
        if(parent == null) {
            files = FileSystemStorage.getInstance().getRoots();
            return new Vector<Object>(Arrays.asList(files));
        } else {
            try {
                files = FileSystemStorage.getInstance().listFiles((String)parent);
            } catch(IOException err) {
                Log.e(err);
                files = new String[0];
            }
        }
        String p = (String)parent;
        Vector result = new Vector();
        for(String s : files) {
            result.add(p + s);
        }
        return result;
    }

    @Override
    public boolean isLeaf(Object node) {
        return !FileSystemStorage.getInstance().isDirectory((String)node);
    }
};
Tree t = new Tree(tm) {
    @Override
    protected String childToDisplayLabel(Object child) {
        String n = (String)child;
        int pos = n.lastIndexOf("/");
        if(pos < 0) {
            return n;
        }
        return n.substring(pos);
    }
};
hi.add(BorderLayout.CENTER, t);
hi.show();

Sample usage of FileSystemStorage & Tree.

From the Codename One project