虚函数实现php版

<?php
class ParentClass {    

  static public function say( $str ) {    
    static::do_print( $str );    
  }    

  static public function do_print( $str ) {    
    echo "<p>Parent says $str</p>";    
  }    

}    

class ChildClass extends ParentClass {    

  static public function do_print( $str ) {    
    echo "<p>Child says $str</p>";    
  }    

}    


class AnotherChildClass extends ParentClass {    

  static public function do_print( $str ) {    
    echo "<p>AnotherChild says $str</p>";    
  }    

}    

echo phpversion();

$a=new ChildClass();

$a->say( 'Hello' );  
$b=new AnotherChildClass();

$b->say( 'Hello' );