PHP development image upload PHP page

This tutorial uses a simple image upload class, the code is as follows

<?php
header("content-type:text/html;charset=utf-8");
class upload
{
var $upload_name;
var $upload_tmp_address;
var $upload_server_name;
var $upload_filetype ;
var $file_type;
var $file_server_address;
var $image_w=900; //要显示图片的宽
var $image_h=350; //要显示图片的高
var $upload_file_size;
var $upload_must_size= 500000; //允许上传文件的大小，自己设置
function upload_file()
{
$this->upload_name =$_FILES["file"]["name"]; //取得上传文件名
$this->upload_filetype = $_FILES["file"]["type"];
$this->upload_server_name = date('y_m_dh_i_s').$this->upload_name;
//    var_dump($this->upload_server_name );
//    exit;
$this->upload_tmp_address = $_FILES["file"]["tmp_name"]; //取得临时地址
$this->file_type = array(
    'image/jpg',
    'image/jpeg',
    'image/png',
    'image/gif',); //允许上传文件的类型
$this->upload_file_size = $_FILES["file"]["size"]; //上传文件的大小
if(in_array($this->upload_filetype,$this->file_type))
{ if($this->upload_file_size < $this->upload_must_size)
{
echo("上传成功，谢谢支持");
$this->file_server_address = "../images/".$this->upload_server_name;
//    var_dump($this->file_server_address );
//    exit;
move_uploaded_file($this->upload_tmp_address,$this->file_server_address);//从temp目录移出
echo("<img src=$this->file_server_address width=$this->image_w height=$this->image_h/>"); //显示图片
}
else
{
echo("文件容量太大");
}
}
else
{
echo("不支持此文件类型，请重新选择");
}
}
}?>

As long as we instantiate this class, we can complete the image upload function