Design Patterns php example code for interface development

<?php
header("Content-type:text/html;charset=utf-8");
/**
* 共同接口
*/
 interface db
{
    function conn();
}

/**
* mysql类
*/
class DbMysql implements db
{
    public function conn()
    {
        echo "连接上了mysql";
    }
}

/**
* sqlite类
*/
class DbSqlite implements db
{
    public function conn()
    {
        echo" Connection on SQLite " ; 
    } 
} 

$ DB = new new DbMysql (); 
$ DB -> Conn (); 

$ DB = new new DbSqlite (); 
$ DB -> Conn ();