All right, 父类postParent定义为抽象，规定子类必须重新实现 buildHTML()方法，这个方法并没有花括号，如果有不管有没有内容都会报错的。
现在越看越觉得这代码完全没必要用抽象类，用继承也都很鸡肋，好吧，也没啥好说的好像。。。。。
另外我把mysql 分开在外面了，所以调用方法很麻烦
1，先实例化 readArticle
2，mysql查询，参数来自 readArticle::getSQL();
3，返回mysql结果资源给 readArticle::fetchResult( $result );
4，readArticle::buildHTML(); 返回HTML
如果是列表循环输出的话，把 3 和 4 重复调用就可以了
abstract class postParent
{
protected $querySQL;
public $fetchResult;
public $timeAgo; // eg : 2 days ago
abstract protected function buildHTML();
public function getSQL()
{
return $this->querySQL;
}
public function fetchResult( $result )
{
$this->fetchResult = mysql_fetch_assoc( $result );
}
public function error()
{}
}
class readArticle extends postParent
{
public function __construct( $id )
{
$this->querySQL =<<<eof
SELECT title, author, text, unixtime FROM post
WHERE id = $id ORDER BY unixtime DESC;
eof;
}
public function buildHTML()
{
return <<<eof
<div id="post-text">
<div class="post-title-div">
<h4>
<a href="http://foodstory.me/post.php?id={$this->fetchResult['id']}"
class="post-title-a" > {$this->fetchResult['title']}
</a>
</h4>
</div>
<div class="post-info-div">
<span class='post-info-author'>{$this->fetchResult['author']}</span> at
<time class='post-info-time'>{$this->timeAgo}</time>
</div>
<div class="post-p-div">
{$this->fetchResult['text']}
</div>
</div>
eof;
}
}