How to custom links aka blogroll widgets?

Question

wordpress\wp-includes\default-widgets.php @ line 91

 /**
 * Links widget class
 *
 * @since 2.8.0
 */
class WP_Widget_Links extends WP_Widget {

 function WP_Widget_Links() {
  $widget_ops = array('description' => __( "Your blogroll" ) );
  $this->WP_Widget('links', __('Links'), $widget_ops);
 }

 function widget( $args, $instance ) {
  extract($args, EXTR_SKIP);

  $show_description = isset($instance['description']) ? $instance['description'] : false;
  $show_name = isset($instance['name']) ? $instance['name'] : false;
  $show_rating = isset($instance['rating']) ? $instance['rating'] : false;
  $show_images = isset($instance['images']) ? $instance['images'] : true;
  $category = isset($instance['category']) ? $instance['category'] : false;

  if ( is_admin() && !$category ) {
   // Display All Links widget as such in the widgets screen
   echo $before_widget . $before_title. __('All Links') . $after_title . $after_widget;
   return;
  }

  $before_widget = preg_replace('/id="[^"]*"/','id="%id"', $before_widget);
  wp_list_bookmarks(apply_filters('widget_links_args', array(
   'title_before' => $before_title, 'title_after' => $after_title,
   'category_before' => $before_widget, 'category_after' => $after_widget,
   'show_images' => $show_images, 'show_description' => $show_description,
   'show_name' => $show_name, 'show_rating' => $show_rating,
   'category' => $category, 'class' => 'linkcat widget'
  )));
 }

 function update( $new_instance, $old_instance ) {
  $new_instance = (array) $new_instance;
  $instance = array( 'images' => 0, 'name' => 0, 'description' => 0, 'rating' => 0);
  foreach ( $instance as $field => $val ) {
   if ( isset($new_instance[$field]) )
    $instance[$field] = 1;
  }
  $instance['category'] = intval($new_instance['category']);

  return $instance;
 }

 function form( $instance ) {

  //Defaults
  $instance = wp_parse_args( (array) $instance, array( 'images' => true, 'name' => true, 'description' => false, 'rating' => false, 'category' => false ) );
  $link_cats = get_terms( 'link_category');
?>
  <p>
  <label for="<?php echo $this->get_field_id('category'); ?>" class="screen-reader-text"><?php _e('Select Link Category'); ?></label>
  <select class="widefat" id="<?php echo $this->get_field_id('category'); ?>" name="<?php echo $this->get_field_name('category'); ?>">
  <option value=""><?php _e('All Links'); ?></option>
  <?php
  foreach ( $link_cats as $link_cat ) {
   echo '<option value="' . intval($link_cat->term_id) . '"'
    . ( $link_cat->term_id == $instance['category'] ? ' selected="selected"' : '' )
    . '>' . $link_cat->name . "</option>\n";
  }
  ?>
  </select></p>
  <p>
  <input class="checkbox" type="checkbox" <?php checked($instance['images'], true) ?> id="<?php echo $this->get_field_id('images'); ?>" name="<?php echo $this->get_field_name('images'); ?>" />
  <label for="<?php echo $this->get_field_id('images'); ?>"><?php _e('Show Link Image'); ?></label><br />
  <input class="checkbox" type="checkbox" <?php checked($instance['name'], true) ?> id="<?php echo $this->get_field_id('name'); ?>" name="<?php echo $this->get_field_name('name'); ?>" />
  <label for="<?php echo $this->get_field_id('name'); ?>"><?php _e('Show Link Name'); ?></label><br />
  <input class="checkbox" type="checkbox" <?php checked($instance['description'], true) ?> id="<?php echo $this->get_field_id('description'); ?>" name="<?php echo $this->get_field_name('description'); ?>" />
  <label for="<?php echo $this->get_field_id('description'); ?>"><?php _e('Show Link Description'); ?></label><br />
  <input class="checkbox" type="checkbox" <?php checked($instance['rating'], true) ?> id="<?php echo $this->get_field_id('rating'); ?>" name="<?php echo $this->get_field_name('rating'); ?>" />
  <label for="<?php echo $this->get_field_id('rating'); ?>"><?php _e('Show Link Rating'); ?></label>
  </p>
<?php
 }
}

How can I construct with this bookmark-template.php so that I can have another custom widgets?

wordpress\wp-includes\bookmark-template.php