PHP設計模式學習筆記： 責任鏈模式（Chain of Responsibility）

// 抽象書本類
abstract class AbstractBookTopic {
    abstract function getTopic();
    abstract function getTitle();
    abstract function setTitle($title_in);
}

// 書本類，繼承自抽象書本類
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 '目前沒有標題';
  }
}

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

}
// 子書本類，繼承自抽象書本類
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;
}

}
// 子子書本類，繼承自抽象書本類
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("開始測試責任鏈模式");
  writeln("");
$bookTopic = new BookTopic("魔法");
  writeln("bookTopic設置標題前:");
  writeln("主題: " . $bookTopic->getTopic());
  writeln("標題: " . $bookTopic->getTitle());
  writeln("");
$bookTopic->setTitle("哈利波特與魔法石");
  writeln("bookTopic設置標題后: ");
  writeln("主題: " . $bookTopic->getTopic());
  writeln("標題: " . $bookTopic->getTitle());
  writeln("");
$bookSubTopic = new BookSubTopic("英國魔法", $bookTopic);
  writeln("bookSubTopic標題設置前: ");
  writeln("主題: " . $bookSubTopic->getTopic());
  writeln("標題: " . $bookSubTopic->getTitle());
  writeln("");
$bookSubTopic->setTitle("哈利波特與混血王子");
  writeln("bookSubTopic標題設置后: ");
  writeln("主題: ". $bookSubTopic->getTopic());
  writeln("標題: ". $bookSubTopic->getTitle());
  writeln("");
$bookSubSubTopic = new BookSubSubTopic("英國現代魔法", $bookSubTopic);
  writeln("bookSubSubTopic標題設置前: ");
  writeln("主題: " . $bookSubSubTopic->getTopic());
  writeln("標題: " . $bookSubSubTopic->getTitle());
  writeln("");
$bookSubTopic->setTitle(NULL);
  writeln("bookSubSubTopic、 bookSubTopic都沒有設置標題:");
  writeln("主題: " . $bookSubSubTopic->getTopic());
  writeln("標題: " . $bookSubSubTopic->getTitle());
  writeln("");
writeln("結束測試責任鏈模式");
function writeln($line_in) {
    echo $line_in.PHP_EOL;
  }</pre>結果： 
開始測試責任鏈模式

bookTopic設置標題前:
主題: 魔法
標題: 目前沒有標題
bookTopic設置標題后: 
主題: 魔法
標題: 哈利波特與魔法石
bookSubTopic標題設置前: 
主題: 英國魔法
標題: 哈利波特與魔法石
bookSubTopic標題設置后: 
主題: 英國魔法
標題: 哈利波特與混血王子
bookSubSubTopic標題設置前: 
主題: 英國現代魔法
標題: 哈利波特與混血王子
bookSubSubTopic、 bookSubTopic都沒有設置標題:
主題: 英國現代魔法
標題: 哈利波特與魔法石
結束測試責任鏈模式</pre>原文地址：http://sourcemaking.com/design_patterns/chain_of_responsibility/php