Question

I have a question which could be language-agnostic but for this particular implementation I’m using Java. It is possible and relatively trivial to list the folders in a directory – using a function like this:

private DefaultMutableTreeNode GenerateFSTree(File f)
{
    int i = 0;
    File[] Children = f.listFiles();

    DefaultMutableTreeNode x = new DefaultMutableTreeNode(f.getName());

    if ( Children != null )
    {
        for ( i = 0; i < Children.length; i++ )
        {
            File f_cur = Children[i];
            if (
            f_cur.isDirectory() && 
            ( this.DisplayHidden || !f_cur.isHidden() ) 
            )
            {   
                x.add(GenerateFSTree(f_cur));
            }
        }
    }

    return x;
}

As you can see this makes heavy use of recursion to evaluate the filesystem and what you end up with is a tree of DefaultMutableTreeNode items.

Now my question is – is there a faster way to do this? There must be, because this is slow. Try executing this on / and it takes forever. Yet if I use say Nautilus or the built-in Java File selection dialog, the tree renders instantly.

So my question is – how can I speed this up?

Thanks

Answer 1

take a look at this example
http://www.java2s.com/Code/Java/Swing-JFC/FileTree.htm
this treemodel will provide the filesystem structure to your jtree. the file system is only accessed when expanding a node… and initially for the root node. 😉

class FileTreeModel implements TreeModel {
    protected File root;
    public FileTreeModel(File root) { this.root = root; }

    public Object getRoot() { return root; }

    public boolean isLeaf(Object node) {  return ((File)node).isFile(); }

    public int getChildCount(Object parent) {
        String[] children = ((File)parent).list();
        if (children == null) return 0;
    return children.length;
    }

    public Object getChild(Object parent, int index) {
        String[] children = ((File)parent).list();
        if ((children == null) || (index >= children.length)) return null;
    return new File((File) parent, children[index]);
    }

    public int getIndexOfChild(Object parent, Object child) {
        String[] children = ((File)parent).list();
        if (children == null) return -1;
            String childname = ((File)child).getName();
            for(int i = 0; i < children.length; i++) {
                if (childname.equals(children[i])) return i;
            }
            return -1;
    }

    public void valueForPathChanged(TreePath path, Object newvalue) {}

    public void addTreeModelListener(TreeModelListener l) {}
    public void removeTreeModelListener(TreeModelListener l) {}


}

usage

Jtree tree = new JTree(new FileTreeModel(new File("/")));

this model will prevent you from filling up your memory with DefaultTreeNodes and minimizes the access to the underlying filesystem.