An example of using classes to bootstrap a WordPress Theme.

class.php

<?php
/**
 * Our main class for our theme.
 * 
 * This will act as our controller, and activate other hooks/functions for wordpress.
 */

class Example {
  
  // Called by our bootstrap_theme function
  public static function init() {
    echo "Hello World";
  }
  
}

functions.php

<?php
/**
 * Our functions file. We're hooking into the wp after_setup_theme 
 * hook to bootstrap our theme, instead of just firing everything 
 * all willy-nilly.
 */

// Bootstrap our theme, this is called by the after_setup_theme hook
function bootstrap_theme {
  
  // Include our class file, which we use to control our theme
  require_once locate_template('/lib/theme/class.php');
  Example::init();
  
}

add_action( 'after_setup_theme', 'bootstrap_theme' );