<?php
/**
 * 抽象状态角色
 */
interface State {
 
  /**
   * 方法示例
   */
  public function handle(Context $context);
}
 
/**
 * 具体状态角色A
 * 单例类
 */
class ConcreteStateA implements State {
  /* 唯一的实例 */
  private static $_instance = null;
 
  private function __construct() {
 
  }
 
  /**
   * 静态工厂方法，返还此类的唯一实例
   */
  public static function getInstance() {
    if (is_null(self::$_instance)) {
      self::$_instance = new ConcreteStateA();
    }
 
    return self::$_instance;
  }
 
  public function handle(Context $context) {
    echo 'Concrete Sate A handle method<br />';
    $context->setState(ConcreteStateB::getInstance());
  }
 
}
 
/**
 * 具体状态角色B
 * 单例类
 */
class ConcreteStateB implements State {
  /* 唯一的实例 */
 
  private static $_instance = null;
 
  private function __construct() {
  }
 
  /**
   * 静态工厂方法，返还此类的唯一实例
   */
  public static function getInstance() {
    if (is_null(self::$_instance)) {
      self::$_instance = new ConcreteStateB();
    }
 
    return self::$_instance;
  }
 
  public function handle(Context $context) {
    echo 'Concrete Sate B handle method<br />';
    $context->setState(ConcreteStateA::getInstance());
  }
 
}
 
/**
 * 环境角色
 */
class Context {
 
  private $_state;
 
  /**
   * 默认为StateA
   */
  public function __construct() {
    $this->_state = ConcreteStateA::getInstance();
  }
 
  public function setState(State $state) {
    $this->_state = $state;
  }
 
  public function request() {
    $this->_state->handle($this);
  }
 
}
 
/**
 * 客户端
 */
class Client {
 
  /**
   * Main program.
   */
  public static function main() {
    $context = new Context();
    $context->request();
    $context->request();
    $context->request();
    $context->request();
  }
 
}
 
Client::main();
?>