private static function _init()
    {
        if (!self::$_isInitialized) {
            self::$_defaultSources = array(
                self::ENVIRONMENT_SOURCE => array(__CLASS__, 'environmentSource')
            );
            self::$_isInitialized  = true;
        }
    }
private static function _init()
    {
        if (!self::$_isInitialized) {
            self::$_defaultSources = array(
                self::ENVIRONMENT_SOURCE => array(__CLASS__, 'environmentSource')
            );
            self::$_isInitialized  = true;
        }
    }
private static function _init ( ) { if ( ! self :: $ _isInitialized ) { self :: $ _defaultSources = array ( self :: ENVIRONMENT_SOURCE => array ( __CLASS__ , 'environmentSource' ) ) ; self :: $ _isInitialized = true ; } }
Initializes the default sources.

@return void
Initializes the default sources .