The difference between new static () and new self () in PHP ____php

The difference between new static () and new self () in PHP

Self: always points to the self code of the class itself, regardless of how many times the class has been inherited, self points to the class that originally used self;
Static: Refers to a class that uses static, and only after inheritance can you show the meaning of a static existence, otherwise static is the same as self.

Class A {
    public  function  getstatic () {return
        new static ();
    }
    Public  function  getself () {return
        new self ();
    }
}
Class B extends a{

}
var_dump ((new B ())->getself ())//a Var_dump ((
new B ())->getstatic ());//b

Questions:
1, do not know what the new static () and new self () have any use;
2. If you want to use new self (), why not use new A ();