The Shipping Container as Object Oriented Code

From the perspective of my daily work, as a web developer, the parallels between shipping containers and object oriented programming are obvious; a standardised design for the shipping of goods across different modes transportation (which interestingly took hold because not only was it standardised, but also it was open - given freely to the ISO standards organisation), which is turned into many many instances of the design (or class), and which is extended in many different ways (inheritance).

<?php
// object oriented presentation of the shipping container:

class shippingcontainer {
public $height;
public $width;
public $length;

private $contents;

function __construct( $height, $width, $length )
{
$this->height = $height;
$this->width = $width;
$this->length = $length;
}

function storeGoods( $goods )
{
$volume = $this->height * $this->width * $this->length;
if ($goods->volume > $volume || isset($contents))
{
    return false;
}
else
{
    $this->contents = $goods->contents;
    return true;
}
}

function unloadGoods()
{
if (!isset($this->contents))
{
    return false;
}
else
{
    $goods = $this->contents;
    unset($this->contents);
    return $goods;
}
}
}

class politicalmeaning extends shippingcontainer
{
public $meaning;

function __construct( $height, $width, $length )
{
$parent::__construct( $height, $width, $length );
$meaning = array();
}

function addMeaning( $new_meaning )
{
$meaning[] = $new_meaning;
}
}

?>