PHP static members

Definition and access of static members ?

Scene one Class

Class

Optimized code

<?php

namespace _1008;

/** *  Just imagine , The following two scenarios : * 1. If an object , We only use it once , Is it still necessary to create objects ,  Directly treat the class as an object , Wouldn't it be more convenient ? * 2. If there are multiple objects ,  You need to share some properties and methods ,  And they must be called by independent objects , Can't share , What do I do ? */

class Demo1
{
    
    //  Instance attributes :  You need to access the object obtained after instantiating the class 
    public $product;

    //  Static members :  attribute ,  Class properties ,  Static attribute 
    public static $price;

    //  Construction method 
    public function __construct($product, $price)
    {
    
        //  References to the current object : $this
        $this->product = $product;
        //  Reference to the current class : self
        self::$price = $price;
    }

    //  In the static method ,  Can I call instance members ?
    public static function test()
    {
    
// return self::$price;
// return $this->product;
    }
}

$obj = new Demo1(' The computer ', 4890);
// ::  Range resolver ,  Class external ,  Use the class name to access static members 
echo  ' Product Name : '. $obj->product, ',  Price : ', Demo1::$price;
//echo '<br>', Demo1::test();
echo '<br>', $obj->test();

Static member call constant

<?php

namespace _1008;

// Class constant 
class Demo2
{
    
    //  Class constant 
    const NATION = ' China ';

    //  Class properties 
    public static $sex;

    public function __construct($sex)
    {
    
        self::$sex = $sex;
    }

    public function get()
    {
    
        return self::NATION;
    }


}

echo Demo2::NATION;
echo '<hr>';
echo Demo2::$sex;
echo '<hr>';
echo (new Demo2(' male '))->get();