Core class used to implement the Toolbar API.
WP_Admin_Bar is WordPress’ class for generating the Toolbar that lines the top of WordPress sites when signed in. This class can be hooked and modified to add or remove options that appear in the admin bar.
The Toolbar replaces the Admin Bar since WordPress Version 3.3.
This class is used internally by WordPress to create an object called $wp_admin_bar. Most modifications to WordPress toolbar will generally be done by modifying the $wp_admin_bar object that is passed through the admin_bar_menu hook.
Example:
add_action( 'admin_bar_menu', 'modify_admin_bar' );
function modify_admin_bar( $wp_admin_bar ){
// do something with $wp_admin_bar;
}