<?php

function my_call_back_function(){

    echo "hello world!";

}

class MyClass{

    static function myCallBackMethod(){

        echo "Hello World!";

    }

}

call_user_func('my_call_back_function');

call_user_func(array("MyClass","myCallBackMethod"));

$obj=new MyClass();

call_user_func(array($obj,"myCallBackMethod"));

call_user_func('MyClass::myCallBackMethod');

class A{

    public static function who(){

        echo "A\n";

    }

}

class B extends A{

    public static function who(){

        echo "B\n";

    }

}

call_user_func(array("B","parent::who"));