那个单例模式做一个Db类,跟tp5 Db静态类一样的功能

<?php
//单例设计模式,不能new 不能clone                  
class Db
{
    private $db_host;//主机名
    private $db_user;//主机账号
    private $db_password;//主机密码
    private $db_name;//选择数据库
    private $db_char;//选择字符集
    private $link;//创建链接对象

    private static $obj = null;

    private function __construct($db_host2,$db_user2,$db_password2,$db_name2,$db_char2)
    {
        $this->db_host = $db_host2;
        $this->db_user = $db_user2;
        $this->db_password = $db_password2;
        $this->db_name = $db_name2;
        $this->db_char = $db_char2;
        $this->connect();
        $this->char();
    }
    public function connect()//链接数据库方法
    {
       $link2 = mysqli_connect($this->db_host,$this->db_user,$this->db_password,$this->db_name);
       $this->link = $link2;//$link赋值成为类的属性,就可以用了
       if(!$this->link)
        {
            echo '链接错误'.mysqli_connect_error();
        }
    }
    public function char()//设置字符集
    {
        mysqli_set_charset($this->link,$this->db_char);
    }

    public function __destruct()//析构方法
    {
        mysqli_close($this->link);//关闭链接
    }

    private function __clone(){}

    public static function getInstance($db_host,$db_user,$db_password,$db_name,$db_char)//传参数进去
    {
        if( !self::$obj instanceof self ) //关键字 instanceof  判断有没有对象
        {
            self::$obj = new self($db_host,$db_user,$db_password,$db_name,$db_char);//new对象和传参
        }
        return self::$obj;
    }
}

$cla = Db::getInstance('127.0.0.1','root','root','test','utf8');

这样静态调用一下就可以使用静态类了