Solution Review: Interfaces

<?php
class User {
    protected $username;
    public function setUsername($name) {
        $this -> username = $name;
    }
    public function getUsername() { 
        return $this -> username; 
    }
}
interface Author {
    public function setAuthorPrivileges($array);
    public function getAuthorPrivileges(); 
}
interface Editor {
    public function setEditorPrivileges($array); 
    public function getEditorPrivileges();
}
class AuthorEditor extends User implements Author,Editor 
{
    private $authorPrivilegesArray = array();
    private $editorPrivilegesArray = array();
    public function setAuthorPrivileges($array) {
        $this -> authorPrivilegesArray = $array;
    }
    public function getAuthorPrivileges() {
        return $this -> authorPrivilegesArray; 
    }
    public function setEditorPrivileges($array) {
        $this -> editorPrivilegesArray = $array;
    }
    public function getEditorPrivileges() {
        return $this -> editorPrivilegesArray; 
    }
}
function test()
{
    $user1 = new AuthorEditor();
    $user1 -> setUsername("Balthazar");
    $user1 -> setAuthorPrivileges(array("write text", "add punctuation")); 
    $user1 -> setEditorPrivileges(array("edit text", "edit punctuation"));
    
    $userName  = $user1 -> getUsername();
    $userPrivileges = array_merge($user1 -> getAuthorPrivileges(), $user1 -> getEditorPrivileges());
    
    echo $userName . " has the following privileges: "; 
    foreach($userPrivileges as $privilege)
    {
        echo " {$privilege},"; 
    }
}
test();
?>