<?php

  class Demo {

    private $_name;

    public function sayHello() {
      print "Hello {$this->getName()}!";
    }

    public function getName() {
      return $this->_name;
    }

    public function setName($name) {
      if(!is_string($name) || strlen($name) == 0) {
        throw new Exception("Invalid name value");
      }

      $this->_name = $name;
    }

  }

?>