封装老是报错搞了两个小时了本人菜鸟各位大神来看看是哪里出

<?php
class PdoMySQL{
public static $config=array();//设置连接参数，配置信息
public static $link=null;//保存连接表示符
public static $pconnect=false;//是否开启长链接
public static $dbVersion=null;//保存数据库版本
public static $connected=false;//判断是否连接成功
public static $PDOStatement=null;//保存PDOStatemen对象
public function _construct($dbConfig=''){
if(!class_exists("PDO")){
self::throw_exception('不支持PDO，请先开启');
}
if(!is_array($dbConfig)){
$dbConfig=array(
'hostname'=>DB_HOST,
'username'=>DB_USER,
'password'=>DB_PWD,
'database'=>DB_NAME,
'hostport'=>DB_PORT,
'dbms'=>DB_TYPE,
'DSN'=>DB_TYPE.":host=".DB_HOST.";dbname=".DB_NAME
);
}
if(empty($dbConfig['hostname']))self::throw_exception('没有定义数据库的配置，请先定义');
self::$config=$dbConfig;
if(empty(self::$config['params']))self::$config['params']=array();
if(!isset(self::$link)){
$configs=self::$config;
if(self::$pconnect){
//开启长连接，添加到配置数组中
$configs['params'][constant("PDO::ATTR_PERSISTENT")]=true;
}
try{
self::$link=new PDO($configs['dsn'],$configs['username'],$configs['password'],$configs['params']);
}catch(PDOException $e){
self::throw_exception($e->getMessage());
}
if(!self::$link){
self::throw_exception('PDO连接错误');
return false;
}
self::$link->exec('SET NAME '.DB_CHARSET);
self::$dbVersion=self::$link->getAttribute(constant("PDO::ATTR_SERVER_VERSION"));
self::$connected=true;
unset($configs);
}
//得到所有记录
public static function getALL($sql=null){
if(!$sql){
self::query($sql);
}
$result=self::$PDOStatement->fetchALL(constant("PDO::FETCH_ASSOC"));
return $result;
}
}
/*自定义错误处理*/
public static function throw_exception($errMsg){
echo '<div style="width:80%;background-color:#ABCDEF;color:black;font-size:20px;padding:20px 0px;">
'.$errMsg.'
</div>'
}
}
?>