/application/models/ToJsonObject.php

<?php
/** 
 * @author davidstockton
 * 
 * 
 */
class Application_Model_ToJsonObject 
{
    public $foo;
    public $bar;
    
    protected $protFoo;
    protected $protBar;
    
    private $privFoo;
    private $privBar;
    
    public function __construct()
    {
        $this->foo = uniqid();
        $this->bar = uniqid();
        $this->protFoo = uniqid();
        $this->protBar = uniqid();
        $this->privFoo = uniqid();
        $this->privBar = uniqid();
    }
    
    public function toJson()
    {
        return Zend_Json::encode(
            array(
                'foo' => $this->foo,
                'bar' => $this->bar,
                'protFoo' => $this->protFoo,
                'privBar' => $this->privBar
            )
        );
    }
}