<?php class CronExpression_FieldFactory { private $fields = array(); public function getField($position) { if (!isset($this->fields[$position])) { switch ($position) { case 0: $this->fields[$position] = new CronExpression_MinutesField(); break; case 1: $this->fields[$position] = new CronExpression_HoursField(); break; case 2: $this->fields[$position] = new CronExpression_DayOfMonthField(); break; case 3: $this->fields[$position] = new CronExpression_MonthField(); break; case 4: $this->fields[$position] = new CronExpression_DayOfWeekField(); break; case 5: $this->fields[$position] = new CronExpression_YearField(); break; default: throw new InvalidArgumentException($position . ' is not a valid position'); } } return $this->fields[$position]; } }