面向对象

什么是面向对象?

我们面对的一切都是对象 ,对象是万物

类的实例化就是对象

继承就是当子类可以继承父类

封装

就是可以把多种方法封装到一个逻辑单元里面

class db{
    protected $host;
    protected $user;
    protected $pas;
    protected $dbname;
    protected $db;

    // 数据库初始化
    function __construct($host = DB_HOST,$user = DB_USER,$pas = DB_PASSWORD,$dbname = DB_DBNAME){
        $this->host = $host;
        $this->user = $user;
        $this->pas = $pas;
        $this->dbname = $dbname;
        if(!$this->db){
            $this->conn();
        }
    }

    // 连接数据库
    function conn()
    {
        $conn = new mysqli($this->host,$this->user,$this->pas);
        if ($conn->connect_error) {
            echo "数据库连接失败,错误信息:" . $conn->connect_error;
        }
        $conn->select_db($this->dbname);
        $conn->set_charset("utf8");
        $this->db = $conn;
    }

以下就是可以写方法  封装一个方法