Revisiting PHP

abstract class Top
{
   public function getOne();
   public function getTwo();
   public function getThree()
   {
      return 300;
   }
}
class Top_extend extends Top
{
   function getOne()
   {
      return 100;
   }
}
//接口
class interface TopInterface
{
   public function getData();
}
class top_interface implements TopInterface
{
}
//$t = new Top(); //抽象类不能被直接实例化
$t = new Top_extend(); //可以通过实例子类

exception.php 异常基类 
//异常基类
class LogException extends Exception
{
var $logfile_dir = 'exception.log';
public function __construct($msg=null,$code=0,$file='')
{
if($file == '')
{
$file = $logfile_dir;
}
$this->saveLog($file);
parent::__construct($msg,$code);
}
//记录日志
protected function saveLog($file)
{
file_put_contents($file,$this->__toString(),FILE_APPEND);
}
}

<?php
//数据库错误类
include_once(&#39;LogException.php&#39;);
class DataBaseException extends LogException
{
protected $databaseErrorMessage;
public function __construct($msg=&#39;&#39;,$code = 0)
{
$this->databaseErrorMessage = $msg;
parent::__construct($msg,$code);
}
public function getMsg()
{
return $this->databaseErrorMessage;
}
}
?>