后期静态绑定

1.传统绑定(self和当前类绑定)

<?php
class User1 extends User
{
    public static $name = '小龙虾';
    public static $money = '38元/斤';
     public static function Demo()
    {
        return self::$name . '现在促销中只需' . self::$money;
    }
}
class User2 extends User
{
    public static $name = '帝王蟹';
    public static $money = '108元/斤';
     public static function Demo()
    {
        return self::$name . '现在促销中只需' . self::$money;
    }
}
echo User::Demo(), '<hr>';
echo User2::Demo();

2.查看把方法放入父类中在子类调用中self和谁绑定

<?php
abstract class User
{
    public static $name = '鲍鱼';
    public static $money = '78元/斤';
    public static function Demo()
    {
        return self::$name . '现在促销中只需' . self::$money;
    }
}
class User1 extends User
{
    public static $name = '小龙虾';
    public static $money = '38元/斤';
}
class User2 extends User
{
    public static $name = '帝王蟹';
    public static $money = '108元/斤';
}
echo User::Demo(), '<hr>';
echo User2::Demo();

由此看出self::总是与声明该方法的类（User）绑定，不与调用类（User1，User2）绑定

3.后期静态绑定（使得声明和调用分开，可以自动与调用类进行绑定）

<?php
abstract class User
{
    public static $name = '鲍鱼';
    public static $money = '78元/斤';
    public static function Demo()
    {
        return static::$name . '现在促销中只需' . static::$money;
    }
}
class User1 extends User
{
    public static $name = '小龙虾';
    public static $money = '38元/斤';
}
class User2 extends User
{
    public static $name = '帝王蟹';
    public static $money = '108元/斤';
}
echo User1::Demo(), '<hr>';
echo User2::Demo();