Java Joe Closures - Quad Tree Example

There has been some discussion about the need for closures in Java, about whether they really would be useful to the great majority of Java programmers. Well I consider myself to write pretty straight-forward Java but I frequently find myself writing this sort of code.

Consider an example from the GIS arena. I have a 'quad-tree' spatial index and I want to be able to add content to the 'quad' that represents a particular lat/long point. I haven't written the quad-tree but it provides a convenience method to find a quad given a lat/long point:

// content to be stored on a quad
public class Content {}
public class Point {}


public class Quad {
   // quad on which content can be stored
  public void add(Content c) {}

  // convenience method for finding the relevant quad in the 
  // quad-tree based on a root quad and a lat/lng
  public void findQuad( 
                  Point pnt,
                  QuadListener listener );
}

// define a listener to be invoked when the correct quad 
// is found
public interface QuadListener {
  void foundQuad( Quad q );
}

If this was Javascript then I could use the classes that I have been supplied with to write a generic addContentToQuadTree() method as below:

function addContentToQuadTree( root,pnt,c ) {
  root.findQuad( pnt,function(q) { q.add(c); } );
}

To do the samething in Java I need to write:

// define a class to hold the content so it can be added to the quad
static class AddContentListener implements QuadListener {
  private final Content c;

  public AddContentListener( Content c ) {
    this.c = c;
  }

  public void foundQuad( Quad q ) {
    q.add( c );
  }
}

// high level method to add the specified content to the 
// quad defined by root and pnt
public void addContentToQuadTree( Quad root, Point pnt, Content c ) {
  root.findQuad( pnt,new AddContentListener( c ) );
}

Closures allow you to avoid defining this intermediate class.