PHP - How To Include Other 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 Guys.. Merry Christmas

Im kinda new to this fantastic world of PHP and i have a little problem i hope you can help me with.

Im trying to build a website where I use include() to genereate my content. On my index.php i have a menu which includes
content in a content div from external .php pages, my structure kinda goes like this.. (simplified)

site/
   index.php
   content/
       fronpage.php
       products.php
       contact.php

The HTML looks like this.

<div id="menu">
    <ul>
          <li><a href="index.php?page=frontpage">frontpage</a></li>
          <li><a href="index.php?page=products">frontpage</a></li>
          <li><a href="index.php?page=contact">frontpage</a></li>
    </ul>         
</div               

<div id="main">

<?php
     include('/content/'.$_GET['page'].'.php');
?>

</div>

This all works very fine, but my problem is, can I have a include inside an already included page?
I would like to have a menu on my products.php site, but that page is already included from above,
and i would like the menu on the products.php site to stay as the content from the nested include
changes with input from the /products folder.

my idea was something like this.

site/
   index.php
   content/
      frontpage.php
      products.php
      contact.php
      products/
         product1.php
         product2.php


the HTML on the index.php is the same as above and then i would add the include() on the
products.php page, so its kinda the same thing, but one inside the other.

HTML inside the products.php folder

<div id="sub_menu">
    <ul>
          <li><a href="#">frontpage</a></li>
          <li><a href="#">frontpage</a></li>
          <li><a href="#">frontpage</a></li>
    </ul>         
</div               

<div id="sub_main">

<?php
     include('/content/products'.$_GET['#'].'.php');
?>

</div>

I dont know how to link to the new files so they will be included while the first include still stays on the page.

Any of you know how and if this can be done? Or maybe at better way to do it?

Hope this made sense, my first PHP question

Thanks

Hi

Still a new comer when it comes to PHP.

I have a situation where I want to use an include within an include and I am having trouble with my file paths.

My main header include, includes everything for each page of my site, beyond the opening of the body to incorporate my navigation etc conditionally loading in css, and loading in titles and meta data etc depending on the page in question.

This header needs to reference another include called the-pod.php which is required for every page, the only trouble is I want to use / to reference the root of the server and this is breaking my code. I can't use ../../ etc as its a different path depending on where the master file is located.

So my question is how do I get around this?

Can the root of the server or path to the root be stored in a variable? and if so how would I write this.

Any tips / advice will be greatly appreciated.

CanI put one INCLUDE statement INSIDE of another INCLUDE statement?