//$this只能用于指向非静态成员
class Demo{
    public $a = 1;
    public function setA(){
        $this->a = 2;
    }
}
//static和self则是指向静态成员
class DemoForStatic{
    public static __construct(){
        static::say();
    }
    public static say(){
        echo 1;
    }
}
class DemoForSelf{
    public static __construct(){
        self::say();
    }
    public static say(){
        echo 1;
    }
}
class A extends DemoForStatic{
    public static say(){
        echo 10086;
    }
}
class B extends DemoForSelf{
    public static say(){
        echo 10086;
    }
}
$a = new A();
$b = new B();