PHP - Understanding Php Classes

I've been spending long hours learning about classes and their magic methods. I just came across a tutorial which showed a constructor like this:

class Device {
    //...
    public function  __construct(Battery $battery, $name) {
        // $battery can only be a valid Battery object
        $this->battery = $battery;
        $this->name = $name;
        // connect to the network
        $this->connect();
    }
    //...
}

the Battery part instantly caught my attention. Here had previously made a Battery class (and a more complete Device class) but the next thing he did really caught my interest:

$device = new Device(new Battery(), 'iMagic');
// iMagic connected
echo $device->name;
// iMagic

what the hell is going on here? Is this another way to include the methods and properties of one class into another class, in order words is this the same thing as:

class Device extends Battery

I don't think so because this new Battery() thing looks more like its creating an object inside the Device object. Previously the only way I could to that was to type $battery = new Battery() inside one of my methods. But this looks like hes doing something different. Can anyone explain whats going on here?   The whole tutorial is he http://code.tutsplus...-php--net-13085 in the main Device method he has a premade $battery variable to hold the Battery object. Sometimes I have multiple classes containing functions which I'd like to include in my main class. I can only extend one class, so I usually extent a class containing only properties, no methods. I still don't know what difference making that info class abstract is, I'd appreciate if anyone could tell me.   Also I'd love to know what the point in static methods is. I've never used them because I've never seen the point. Is it just to make it easier to call the methods because you don't need to create an object instance to call them? Sorry for the extra questions, the first one is what I'm really wondering about.    

Not sure how to describe what I'm trying to do here in the title, but here goes with what I am trying to accomplish.

I've got a few hundred lines of code in total so far, so I'll try to keep it as short as I can. I've got an application that I am programming using classes for each module and right now I am coding the base classes that I need in order for it to run (database, errors, logging, etc). What I'm doing for my database class is I have a query factory and it extends the MySQLi class so I can process, clean and code the rest of my app faster. I also have another, unrelated class "Error", which will be used for processing errors I might come across.

I'd rather do it this way instead of having to call trigger_error and error_log every time there is an error. I'd also not like to have to call a new instance of an object every time I need to use something from that class. Is there any way I can call a class within a class and return it as an object for all the methods within the class?

I've tried the methods below, but no luck I've tried others, but I'm trying to keep it brief and get what I'm trying to do across.

<?php

class QueryFactory extends MySQLi {

public  $err = new error(); //Doesn't work.
public  $err = error(); //Nope.

#This is the function that I need the $err object for.
function set($fields, $newvals) {

if ( is_array($fields) && is_array($newvals) ) {

if ( count($fields) != count($newvals) ) {
//Instead of below, I want to do something like $err->('Array lengths must match for method', 256, $islogged = 1);
                              trigger_error('Array lengths must match for method', 256);
}

}
}

}


The thing is, I have a "run.inc.php" which does include and create new objects for running just the basic app and if I try to redeclare the error class in query.class.php, it gives me an error saying I can't do that, but if i try to call $err from the page that has all the classes defined it throws an error saying that my method is undeclared. I'd like my error class be available to every other class I create so I can display and log errors as needed. Any suggestions or links to point me where I'd like to go?

Hi, can someone help me figure out why the logo div isn't centering? 

Code: [Select]
<?php
require_once("functions.php"); 
?> 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Untitled Document</title>
<style type="text/css">
td {
border-top-style: solid;
border-right-style: solid;
border-bottom-style: solid;
border-left-style: solid;
border-top-color: #30C;
border-right-color: #30C;
border-bottom-color: #30C;
border-left-color: #30C;
}
</style>
<link href="doggyTreats.css" rel="stylesheet" type="text/css" />
</head>

<body>

<?php
[color=yellow]logo();[/color]
navBar();
echo "<div id=\"mainContent\">";
echo "<form action=\"\" method=\"post\" name=\"catalog\">";
  
DatabaseConnection();  

  $query = "SELECT * FROM treats"; 
        $result_set = mysql_query($query) or die(mysql_error());
$i = 0;

        echo "<table>";
        while ($row = mysql_fetch_array($result_set))
        {
echo"<tr><td width=\"2s00px\"><img src=\"{$row['product_pic']}\" /></td><td width=\"200px\">{$row['product_title']}.<br /><br />{$row['product_Description']}.<br /> Price:  \${$row['price']}.<br /><br />Quantity <input name=\"quantity\" type=\"text\" size=\"2\" /></td></tr>";
        }
echo "<tr>"; 
echo "<td><input name=\"submit\" type=\"button\" value=\"Proceed to Checkout\" />"; 
echo "</table>";    
echo "</form>";
echo "</div>";
footer();
?>
</body>
</html>

Code: [Select]
#navBar {
background-color: #060;
width: 200px;
padding-top: 50px;
padding-bottom: 250px;
float: left;
}
#navBar #menu {
margin-right: 6px;
}

.menuOption {
background-image: url(assets/bone2a.gif);
background-repeat: no-repeat;
padding-bottom: 25px;
list-style-type: none;
height: 20px;
padding-top: 26px;
text-align: center;
}
body {
background-color: #0089cc;
}[color=yellow]
#logo  {
text-align: center;
margin-top: 5px;
height: 123px;
width: 182px;
}[/color]
#footer {
font-style: italic;
text-align: center;
}
.shoppingCart tr th {
padding: 5px;
}
.shoppingCart tr td {
padding: 5px;
}
#mainContent {
width: 350px;
margin-top: 30px;
}


Code: [Select]
<?php
[color=yellow]function logo()
{
echo "<div id=\"logo\">";
echo "<img src=\"assets/logo.gif\" alt=\"logo\" />"; 
echo "</div>";
}[/color]
function footer()
{
echo "<div id = \"footer\">";
echo "Auntie Vic\'s Treatery <br />";
echo "PO Box 34092 <br />";
echo "Clermont, IN 46234 <br />";
echo "317-701-0343 <br />";
echo "<a href=\"mailto:auntievics@gmail.com\">Email Us</a>";
echo "</div>";
}  
function navBar()
{

    echo "<div id = \"navBar\">";
echo "<ul id=\"menu\">";
echo "<li class=\"menuOption\"><a href=\"index.html\">Home</a></li>";
echo "<li class=\"menuOption\"><a href=\"aboutUs.html\">Management Team </a></li>";
  echo "<li class=\"menuOption\"><a href=\"treats.html\">Treats </a></li>";
echo "<li class=\"menuOption\"><a href=\"charities.html\">Supported Charities</a></li>";
echo "<li class=\"menuOption\"><a href=\"order.html\">Orders</a></li>";
echo "</ul>";
echo "</div>";
}
?>

I have a system that I want to change. 

I'm attempting to convert a huge project I made with mysql to PDO.  I have many cases where I would use a WHILE statement to return a query array.
Code: [Select]
while($row= mysql_fetch_array($result)){From what I've seen so far, it looks as though I need to use a foreach statement to do the same task.
Code: [Select]
foreach ($dbh->query($sql) as $row){
Is that correct?