<?php

class Father
{
   public static function money()
   {
      return __CLASS__.'\'s money';
   }
 
   public static function life()
   {
      return static::money();
   }
}
 
class Son1 extends Father
{
   public static function money()
   {
      return __CLASS__.'\'s money';
   }
}
 
class Son2 extends Father
{
}

printf("%s\n%s", Son1::life(), Son2::life());
   
 
// Output  
$ php -f test.php
Son1's money
Father's money