// 抽象书本类
abstract class AbstractBookTopic {
    abstract function getTopic();
    abstract function getTitle();
    abstract function setTitle($title_in);
}

// 书本类，继承自抽象书本类
class BookTopic extends AbstractBookTopic {
    private $topic;
    private $title;

    function __construct($topic_in) {
      $this->topic = $topic_in;
      $this->title = NULL;
    }

    function getTopic() {
      return $this->topic;
    }

    function getTitle() {
      if (NULL != $this->title) {
        return $this->title;
      } else {
        return ‘目前没有标题‘;
      }
    }

    function setTitle($title_in) {
      $this->title = $title_in;
    }
}

// 子书本类，继承自抽象书本类
class BookSubTopic extends AbstractBookTopic {
    private $topic;
    private $parentTopic;
    private $title;

    function __construct($topic_in, BookTopic $parentTopic_in) {
      $this->topic = $topic_in;
      $this->parentTopic = $parentTopic_in;
      $this->title = NULL;
    }

    function getTopic() {
      return $this->topic;
    }

    function getParentTopic() {
      return $this->parentTopic;
    }   

    function getTitle() {
      if (NULL != $this->title) {
        return $this->title;
      } else {
        return $this->parentTopic->getTitle();
      }
    }

    function setTitle($title_in) {
      $this->title = $title_in;
    }
}

// 子子书本类，继承自抽象书本类
class BookSubSubTopic extends AbstractBookTopic {
    private $topic;
    private $parentTopic;
    private $title;

    function __construct($topic_in, BookSubTopic $parentTopic_in) {
      $this->topic = $topic_in;
      $this->parentTopic = $parentTopic_in;
      $this->title = NULL;
    }

    function getTopic() {
      return $this->topic;
    }

    function getParentTopic() {
      return $this->parentTopic;
    }   

    function getTitle() {
      if (NULL != $this->title) {
        return $this->title;
      } else {
        return $this->parentTopic->getTitle();
      }
    }

    function setTitle($title_in) {
      $this->title = $title_in;
    }
}

  writeln("开始测试责任链模式");
  writeln("");

  $bookTopic = new BookTopic("魔法");
  writeln("bookTopic设置标题前:");
  writeln("主题: " . $bookTopic->getTopic());
  writeln("标题: " . $bookTopic->getTitle());
  writeln("");

  $bookTopic->setTitle("哈利波特与魔法石");
  writeln("bookTopic设置标题后: ");
  writeln("主题: " . $bookTopic->getTopic());
  writeln("标题: " . $bookTopic->getTitle());
  writeln("");
 
  $bookSubTopic = new BookSubTopic("英国魔法", $bookTopic);
  writeln("bookSubTopic标题设置前: ");
  writeln("主题: " . $bookSubTopic->getTopic());
  writeln("标题: " . $bookSubTopic->getTitle());
  writeln("");

  $bookSubTopic->setTitle("哈利波特与混血王子");
  writeln("bookSubTopic标题设置后: ");
  writeln("主题: ". $bookSubTopic->getTopic());
  writeln("标题: ". $bookSubTopic->getTitle());
  writeln("");
 
  $bookSubSubTopic = new BookSubSubTopic("英国现代魔法", $bookSubTopic);
  writeln("bookSubSubTopic标题设置前: ");
  writeln("主题: " . $bookSubSubTopic->getTopic());
  writeln("标题: " . $bookSubSubTopic->getTitle());
  writeln("");

  $bookSubTopic->setTitle(NULL);
  writeln("bookSubSubTopic、 bookSubTopic都没有设置标题:");
  writeln("主题: " . $bookSubSubTopic->getTopic());
  writeln("标题: " . $bookSubSubTopic->getTitle());
  writeln("");

  writeln("结束测试责任链模式");

  function writeln($line_in) {
    echo $line_in.PHP_EOL;
  }

开始测试责任链模式

bookTopic设置标题前:
主题: 魔法
标题: 目前没有标题

bookTopic设置标题后: 
主题: 魔法
标题: 哈利波特与魔法石

bookSubTopic标题设置前: 
主题: 英国魔法
标题: 哈利波特与魔法石

bookSubTopic标题设置后: 
主题: 英国魔法
标题: 哈利波特与混血王子

bookSubSubTopic标题设置前: 
主题: 英国现代魔法
标题: 哈利波特与混血王子

bookSubSubTopic、 bookSubTopic都没有设置标题:
主题: 英国现代魔法
标题: 哈利波特与魔法石

结束测试责任链模式