Tag Archive for 'PHP OOP'

Sandlight CMS III: PHP Abstract Factory

abfacNote: This is the third in a series for developing a CMS for Sandlight Productions. Drop by the Sandlight site to see the progress so far, and be sure to check your country’s flag count!

Now that the CMS has a filter for different devices, it now needs a pattern to take care of those devices and different types of content that they will display. Previous posts on this blog used the Bridge pattern and the Factory Method pattern. However, another pattern might be more useful for all of the different things that a Content Management System (CMS) might do. A review of the series of posts on this blog for how to select a design pattern, shows the different criteria to consider. The CMS has to create different elements of a Web page for different devices and that fact must be the focal point of the consideration. The section head for Creational Patterns in Learning PHP Design Patterns, lists the Abstract Factory pattern as a creational one, but that pattern was not discussed in the book nor on this blog. It would appear to be just what this CMS needs.

The Abstract Factory Design Pattern

The Abstract Factory pattern has features for families of factories and products instead of individual factories as does the Factory Method pattern. In comparing the relatively simple Factory Method pattern with the Abstract Factory, the Abstract Factory has multiple abstract product interfaces with multiple concrete factories for the families of the products.

Figure 1 shows the the Abstract Factory class diagram, and when you look at it, try to focus on the fact that the pattern has two types of interfaces: Factory and Product. So, if you understand the Factory Method pattern, you have a starting point for appreciating the Abstract Factory:

Figure 1: Abstract Factory class diagram

Figure 1: Abstract Factory class diagram

Unlike the Factory Method pattern, the Abstract Factory includes a Client class as an integral part of the pattern. Further, the Client holds an association between both the AbstractFactory (AbsFactory) and the two AbstractProduct classes. So while it shares some of the basic Factory Method characteristics, it is clearly a different pattern than the Factory Method.

Since the Abstract Factory may appear to be daunting, the color-coded the product instantiations (dashed lines) in the file diagram (appearing in the Play window) help show where each concrete factory method calls. Experiment with different combinations of factories (devices) and products (page parts) and look at the diagram so that you can see the path. Phone instantiations are in green, Tablet in red, and Desktop in blue. Experiment with the different single products first, and then click the bottom button to see what different “pages” each device factory displays.

Implementing the Abstract Factory in PHP

To see how this implementation of the Abstract Factory design pattern works, click the Play button. You will see both the interactive Abstract Pattern tester and the of the file diagram of this implementation of the Abstract Factory for the evolving Sandlight CMS. Click the Download button to see all of the files in the diagram. For this particular post, downloading all of the files is more important than usual because there are lots of them, and rather than having listings for all in this write-up, I’ve just selected representative ones.
PlayDownload

In addition to the Abstract Factory file diagram (viewed when you click the Play button), the following quick overview of the participants’ roles and how the CMS implements the Abstract Factory explain how this implementation works:

Client client: Only uses interfaces declared by IAbFactory (interface) and IProducts (abstract classes IHeaderProduct, IImageProduct and ITextProduct.) This means that the Client can only use the classes and methods implemented from those two interface types—factory or products. In other words, it should not directly implement a product (a page element) by directly using a product independent of the factory and product interfaces. Figure 2 illustrates this point:

Figure 2: Client works through Abstract Factory implementations

Figure 2: Client works through Abstract Factory implementations

In going over the other participants below, keep in mind that the Client can only implement concrete implementations of the IAbFactory to request products (page parts for different devices.)

IAbFactory interface: Establishes the methods for the concrete factories.

  • PhoneFactory implements operations to create phone products
  • TabletFactory implements operations to create tablet products
  • DesktopFactory implements operations to create desktop products

IHeaderProduct: abstract class Establishes the method for concrete header products and adds protected property for returning completed product.

  • PhoneHeader defines phone object to be created by the PhoneFactory and
    implements the IHeaderProduct interface
  • TabletHeader defines tablet object to be created by the Tabletactory and
    implements the IHeaderProduct interface
  • DesktopHeader defines desktop object to be created by the DesktopFactory and
    implements the IHeaderProduct interface

IImageProduct: abstract class Establishes the method for concrete image and/or video products and adds protected property for returning completed product.

  • PhoneImage defines phone object to be created by the PhoneFactory and
    implements the IImageProduct interface
  • TabletImage defines tablet object to be created by the Tabletactory and
    implements the IImageProduct interface
  • DesktopImage defines desktop object to be created by the DesktopFactory and
    implements the IImageProduct interface

ITextProduct: abstract class Establishes the method for concrete text products and adds protected property for returning completed product.

  • PhoneText defines phone object to be created by the PhoneFactory and
    implements the ITextProduct interface
  • TabletText defines tablet object to be created by the Tabletactory and
    implements the ITextProduct interface
  • DesktopText defines desktop object to be created by the DesktopFactory and
    implements the ITextProduct interface

Comparing the above outline with the Abstract Factory file diagram (seen when you click the Play button) shows that the Abstract Factory is bound to the idea of a factory implementing a product. The specific classes (products) requested are never directly referenced by the Client; rather it is through a factory. The CMS application requires factories for the different device categories; Phone, Tablet and Desktop. Each factory should be able to build the necessary parts (products) for each device. In this case (and for this example) the products are a Header, Graphic and Text. Each factory can build its own version of the products; so requesting a header, for example, is through a concrete factory, and depending on which concrete factory the clients requests, it builds the appropriate product.
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Sandlight CMS II : Mobile First!

mobileFirstI’m not a graphic designer, and so I depend on others for the graphic elements and arrangement of my Web pages. However, I strive to make a site that is clear, easy to understand and useful. My focus is on good user experience (UX) and information design—clear communication with the user. In order to have good UX, you need to know something about Responsive Web Design (RWD), and if you don’t, check out the RWD link. Further, if you are unfamiliar with the approaches to RWD, I’m sold on the Mobile First approach, but possibly for different reasons than designers. Let me explain.

In designing my own site, my focus is on content categories, ease of maintenance, which includes updates and changes, and device flexibility. So I have to keep all of those in mind. I want PHP to handle regular updates by using content from a MySql database (the Content Management of CMS), and I need it to work on different devices. By tackling mobile first, I have to create a diamond-tipped focus on exactly what I want the user to view because even with the new “Phablets,” I’m not dealing with a lot of screen real estate. Currently, my old working mobile phone has a CSS resolution of 320 x 480, and my Phablet is 414 x 736. That’s less that 100 units different. (By CSS resolution, I’m referring to what CSS reads as far as screen width is concerned. See this table.)

Choosing the Devices

In an another sniffer program using a Chain of Responsibility (CoR) design pattern and a PHP user agent ($_SERVER['HTTP_USER_AGENT']) posted on this blog, the sniffer detected the user agent and then found the handler responsible for that agent. Now that user agents have been replaced by CSS screen width (as determined by a JavaScript function) for determining the device, we can use the same CoR pattern making the necessary changes. However, instead of getting real pages, we can use stand-ins that only have the roughest page content. All of the content will be encapsulated into PHP classes using heredoc strings. Near-future posts cover the mechanics of working out the MySql to provide dynamic content for the pages, along with other details necessary for the CMS. For now, though, the dummy pages will only contain enough material to demonstrate that each is appropriate for the selected device. Use the buttons below to see the current state of the CMS and download the files for this portion:
PlayDownload

Note that all devices can now access the Flag Counter. Where is your country on the Flag Counter? (See the note about the Flag Counter at the end of this post.)

Back to the Chain of Responsibility Pattern (CoR)

The CoR pattern is handy because it’s easy to update and change. For example, suppose that having three device categories (e.g., phone, tablets and desktops) proves to be inadequate and you want to add two more; one for laptops and another for phablets. It’s a simple matter to add to the chain and add device classes to handle the new devices. Figure 1 shows the first design pattern to be used in the CMS:

Figure 1: Chain of Responsibility Implementation

Figure 1: Chain of Responsibility Implementation

In Part I of this series, you can see how the device width and height is determined using a JavaScript closure (object) to pass the information to HTML and on to PHP. Since we only need to find the width, the JavaScript code has been slightly altered and placed in a separate file (deviceCatcher.js) in case it needs to be reused.

?View Code JAVASCRIPT
//deviceCatcher.js
function getWide()
{
	var wide = screen.width;
	return function()
	{
		return wide;
	}
}
var w = getWide();
//Send data to PHP class, CoRClient.php	
var lambdaPass= function() {window.location.href = "CoRClient.php?hor=" + w();};

The HTML file simply calls the closure function which passes the values to PHP:

<html>
	<head>
		<title>Device Catcher</title>
		<script src="deviceCatcher.js" type="text/javascript"></script>
	</head>
	<body onload=lambdaPass()>
	</body>
</html>

The HTML file is a trigger to get the ball rolling with the client class (CoRClient).

Starting the Chain

The client pulls the viewing device’s width from the superglobal, and passes it to a PHP variable. Given the variability in the width of device screens, I made the decision to work with three sizes to get started: 1) phone, 2) tablet, and 3) desktop. So, depending on the width, the request would be handled by one of those three device groups. I used the following cutoff sizes:

  1. Phone: >= 480
  2. Tablet: >=481 and < 900
  3. Desktop: >= 900

I used this table as a guide, but cutoff points can be anything you want.

Getting the width from the superglobal is easy enough using a static variable:

self::$wide=$_GET['hor'];

The, using the cutoffs, the program needs to generate three strings, phone, tablet, and desktop to send to the Request class that stores the appropriate string. The most obvious way is to use conditional statements (if or switch) to generate the correct string for Request. For example an imperative algorithm such as the following would do the trick:

if(self::$wide < = 480)
{
	return "phone";
}
elseif (self::$wide >= 900)
{
	return "desktop";
}
else
{
	return "tablet";
}

However, a functional program would be more compact, and like the JavaScript closure used in Part I, it would be an “object.” Transformed into a functional closure, the operation would look like the following:

$beta = self::$wide >= 900 ? 'desktop' : 'tablet';
$lambda = function($x) use ($beta) {
	$alpha =  $x < = 480 ? 'phone' : $beta;
	return $alpha;};

Using ternary operations ?: , $alpha and $beta both have function-like qualities. for example, $beta could have been written as a function beta() as shown in Figure 2:

Figure 2: "Functional" variables

Figure 2: “Functional” variables

As you can see in Figure 2, $beta provides the same functionality as beta(), and $beta can be used as a reference in the $lambda function along with $alpha in a PHP closure. (For some reason, when $beta is assigned an anonymous function, I was unable to get it to be added as a closure in the $lambda anonymous function.)
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PHP Class Origins: An OOP Job for the HTML UI

couchPotatoPutting HTML to Work

At some point in OOP development with PHP, I quit putting little PHP code snippets in HTML. I either left all PHP out of HTML or encapsulated HTML in a PHP heredoc string inside a class. In that way, all PHP would be part of an OOP order without any loose ends. That may seem overly fussy, but it avoids the slippery slope of degenerating back into sequential programming——patchwork quilt programming.

However, such a practice should not disallow HTML from helping out in an OOP project. A lot of times, I found myself sifting through class and method options using more conditional statements than I wanted in the Client. I realized that I could just pass the class name directly to the Client from a superglobal with origins in an HTML input form. Likewise, I could do the same for methods, and this has become a useful standard operating procedure.

To better illustrate using the HTML UI in launching a selected class object, the following application uses the color and number input elements with both class and method information stored in HTML element values. Both are trivial, but help illustrate the point: (Use Firefox, Chrome or Opera–neither Safari nor Internet Explorer implemented the HTML5 standard color input element.)
PlayDownload

It’s odd in a way that PHP developers (myself included) are so used to using HTML UIs for data input into MySql databases or making other choices, but few use the UI for calling classes and methods. However, it’s both easy and practical.

Where to Put the OOP in HTML?

You can place class and method names as values anywhere in form inputs that you’d put any data passed to PHP as superglobals. One input form I found useful is the hidden one. It’s out of the way, and you can build forms around the class with other superglobal inputs as methods. Using radio button inputs is another nice option because you can use them either for calling classes or methods with the mutual exclusivity assurance of knowing that not more than one will be called from a given group. To get started, take a look at the HTML:

< !DOCTYPE html>
<html>
<head>
    <link type="text/css" rel="stylesheet" href="tech.css"/>
    <title>Unsetting Superglobals with Classes and Methods</title>
</head>
 
<body>
    <h3>Classes and Methods</h3>
<form name="alpha" action="Client.php" method="post" target="feedback">
    Choose color from the color window:<br />
    <input type="hidden" name="class" value="ColorClass"/>
    <input type="hidden" name="method" value="doColor"/><br />
    <input type="color" name="colorNow" value="#cc0000"/>
    <p>
    <input type="submit" value="Get Color"/>
    </p> 
</form>
<form name="beta" action="Client.php" method="post" target="feedback">
    Divide or modulo the following two numbers:<br />
    <input type="hidden" name="class" value="MathClass"/>
    First:&nbsp;<input type="number" name="first" value=2/>&nbsp;
    &nbsp;Second:&nbsp;<input type="number" name="second" value=7/>
 
    <br /><input type="radio" name="method" value="doDivide"/>
    &nbsp;Divide the second by the first<br />
    <input type="radio" name="method" value="doModulo" checked=true/>
    &nbsp;Modulo the second by the first<br />
    <p>
    <input type="submit" value="Do Math"/>
    </p> 
</form>
<iframe name="feedback">feedback</iframe>
</body>
</html>

The code has two forms, alpha and beta, and you can think of them as I/O for two different classes. The feedback is returned to the iframe named feedback. Both forms have the action calls to Client.php. So the general plan is:

Client → Class->method()

In the alpha form, the class is ColorClass and the method is doColor()—both in hidden input elements. The name for the class element is “class” and the name for the method element is “method.” All the user does is to choose a color that is passed through the superglobal associated with the color input element.

In the beta form, the class is MathClass placed in a hidden input element. The user chooses either a division or modulo operation from the two radio input elements where the names of the appropriate methods are stored. Once again, the name for the class element is “class” and with mutually exclusive choices the radio button elements for selecting the method, the name is “method.” In this way, whatever superglobal named “class” will fire the correct class and call the correct method with the superglobal named “method.”

The Client

As usual, the Client is the launching pad for the operations. If your application uses different client classes depending on user choices, it’s an easy matter to have unique client names for different forms. In this particular case, the Client class doesn’t care about the form of origin for the request. It just takes the class superglobal and method superglobal names and generates a call to the appropriate class and method.

As an aside, the Client in OOP should not be as rare as some perceive it to be. In one way or another, users (or non-human request mechanisms) employ some way to request that the software do something. The Client, as a participant in a structure, is in virtually every design pattern in one way or another. Even when the Client is not directly or implicitly in a design pattern, The Gang of Four reference it as related to one of the participants in the pattern. So while this example does not use a design pattern, the Client works perfectly well in any OOP program.

< ?php
/*
 * Set up error reporting and
 * class auto-loading
*/
error_reporting(E_ALL | E_STRICT);
ini_set("display_errors", 1);
// Autoload given function name.
function includeAll($className)
{
    include_once($className . '.php');
}
//Register
spl_autoload_register('includeAll');
 
//Class definition
class Client
{
    private static $object, $method;
    //client request
    public static function request()
    {  
        self::doSuper();
        $operation = new self::$object();
        echo $operation->{self::$method}();
    }
 
    private static function doSuper()
    {
        self::$object = $_POST['class'];
        self::$method=$_POST['method'];
        unset($_POST['class']);
        unset($_POST['method']);
    }
}
Client::request();
?>

The Client file first takes care of error reporting and automatically calling classes. One experienced developer told me that adding an error-reporting function was unnecessary because it could be automatically turned on in the php.ini file. That’s true, but since I work with many different PHP environments where I have no control over the php.ini file, I’ve found it to be a good practice. You only have to put it in once place, and it takes care of error reporting for the entire program. Besides, I found that one safeguard against easy hacking is to turn off error reporting so that hackers cannot see the names of the classes involved in the application. For this blog, though, I leave the error reporting on because there’s nothing on this blog I want to hide. (Change the init_set from “1” to “0” to turn off all error-reporting.)

No Returns from Constructor Functions

The first incarnation of this application used the same two forms, but the alpha form only had the class name with the results planned to be sent back for output using a return statement. I kept getting errors, and then I learned that constructor functions (those using the __construct() method) have no returns. All they do is to instantiate the class. If you do not use the __construct() method, there’s an invisible automatic constructor function that does that for your as soon as you call new ClassName().
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PHP OOP & Algorithms II: What to Use

algorithm2What Are the Guidelines?

Like just about everything else in computing, there’s a certain amount of empirical testing. More importantly, however, are the general principles derived by both empirical and mathematical calculations. In the first post on algorithms and OOP, you saw an example that showed how many operations were necessary to find “Waldo,” a name near the end of an array of over 1,000 elements. One used a straight up loop and the other a binary search algorithm. Both were pretty quick; in fact it was hard to tell the difference in speed, and without seeing the little dots, you would not have seen the number of iterations required in each algorithm. You also saw that quadratic algorithms grew at rates that can quickly reach a point where processing comes to a crawl.

A Table Guide

Table 1 is derived from the 4th Edition of Algorithms (2011, p. 187) by Robert Sedgewick and Kevin Wayne. I’ve summarized it further. (Examples in the book are all in Java.) It is a rough but useful guide, and I have found it handy for a quick look-up.

Table 1: Algorithm Order of Growth

NameOrder of GrowthDescriptionExample
 constant 1statement   2 + 7
 logarithmic log Ndivide in half   binary search
 linear Nloop   find max
 linearithmic N log Ndivide & conquer   mergesort
quadratic N²double loop   check all pairs
cubic N³triple loop   check all triples
exponential2Nexhaustive search   check all subsets

Fortunately, most of the time our algorithms are pretty simple statements, single loops or recursive calls. All of the models in green are algorithms we should try and stick with. You should avoid the reds ones if possible.

What About Recursive Algorithms?

Those who love to profess a little knowledge like to say that recursion is slower than a loop. As indicated, we really don’t want to end up paying attention to small costs. Recursion is important, and using recursive algorithms is cost effective, especially since the difference in running time is negligible.

We often use recursive implementations of methods because they can lead to compact, elegant code that is easier to understand than a corresponding implementation that does not use recursion.
~Robert Sedgewick and Kevin Wayne

(A recursive example of a logarithmic algorithm is not included here, but you can find a recursive binary search in the post on binary searches.) What we need to pay attention to are the order-of-growth issues. For example, quadratic algorithms on the lower end of the scale are not really that bad, but when the N increases at a squaring rate, it’s easy to run into problems. So if you avoid quadratic algorithms, you’ll be better off when the N increases. On the other hand, whether you’re using a recursive method for a binary search, you’ll not see that much of a difference as the N increases compared to non-recursive methods.

A Strategy Design Pattern Handles Algorithms

This blog has lots of posts detailing the Strategy design patterns; so if you’re not familiar with a PHP implementation of the Strategy pattern, you might want to take a quick look at the code. To get started, play the example and download the code.
PlayDownload

In the last post on algorithms, the program used a Factory Method pattern to produce an array, and in this post, the same pattern is used and two additional array products have been added. However, instead of having the algorithm classes be more or less on their own, all of the algorithm classes have been organized into a Strategy design pattern. Figure 1 is a file diagram of the objects in the application:

Figure 1: Object groupings with Strategy and Factory Method patterns

Figure 1: Object groupings with Strategy and Factory Method patterns

If Figure 1 looks a bit daunting, it is only three object groupings. The HTML and PHP Client make a request for one of seven algorithm implementations through a Strategy pattern. The concrete strategy implementations all get their data from a “data factory.” Figure 2 provides an easier (and more accurate) way to understand what’s going on.

Figure 2: Overview of the main purposes of the objects.

Figure 2: Overview of the main purposes of the objects.

So instead of having a complex task, you only have three groupings of classes and interfaces: Those making a request (Clients), those executing operations on data (Algorithms) organized as a Strategy pattern and the data itself organized with a Factory Method (Data.)

Figure 2 shows a simplified version of what the program does. The Context class considerably eases the requesting process. The HTML UI passes the name of the requested concrete strategy to the Client, and the Client uses the name as a parameter in a Context method. The Client is not bound to any of the concrete strategies because the strategy classes are handled by a Context object and method. (Click continue to see the PHP implementations of the algorithms.)
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PHP OOP & Algorithms I: An Introduction

quadAvoiding the Misinformed

Programmers often spend more time un-doing bad information than using good information. One of the comments that set me off recently was someone “explaining” to others on a blog why PHP was not an object oriented language. Then he continued to blather on about the difference between compiled and interpreted languages. Whether or not a language is compiled or not has nothing to do with whether or not it is an object oriented language. Having interfaces, classes and communication between objects are the key criteria of an OOP language, and certainly since PHP5 has been a full-fledged OOP language. (We PHPers should not feel singled out because I recently saw post where a Java programmer pronounced that neither Python nor Perl were OOP, and she was “informed” otherwise by irate Python programmers. Perl has been OOP since V5.) So here I am again wasting time grumbling about people who don’t know what they’re talking about.

Instead of frothing at the mouth over the misinformed, I decided to spent more time with the well-informed. To renew my acquaintance with algorithms I began reading Algorithms 4th Ed. (2011) by Sedgewick and Wayne. Quickly, I learned some very basic truths about algorithms that had been only vaguely floating around in my head. First and foremost are the following:

Bad programmers worry about the code.
Good programmers worry about data structures and their relationships.
Linus Torvalds (Creator of Linux)

Since we’ve been spending time on this blog acting like good programmers, that was reassuring. In this post, I’d like to look at two things that are important for developing algorithms: 1) What to count as a “cost” in developing algorithms, and 2) Identifying good and bad algorithmic models. First, though, play and download the example. Using two different algorithms, a logarithmic and a linear (both pretty good ones), I’ve added “dots” to loop iterations to visually demonstrate the difference between a logarithmic algorithm (binary search) and a linear algorithm (loop). The “expense” of the algorithm can be seen in the number of dots generated.
PlayDownload

The example is a pretty simple one. However, since this blog is about PHP Design Patterns, I added a little Factory Method. The two algorithm classes act like clients making requests through the factory for a big string array with over 1,000 first names. Figure 1 shows the file diagram:

Figure 1: File diagram for use of Factory Method by two algorithm clients.

Figure 1: File diagram for use of Factory Method by two algorithm clients.

In looking at the file diagram, you may be thinking, “Why didn’t you use a Strategy pattern coupled with that Factory Method?” I thought about it, but then decided you could do it yourself. (Why should I have all the fun?)

Lesson 1: Leave the Bag of Pennies

The first lesson I learned in Bank Robbery 101 was to leave the bag of pennies. They’re just not worth it. Speed is everything in a bank robbery, and so you pay attention to how to get the most with the least time. The same thing applies to analyzing algorithms. For example, an object (as compared to an integer, boolean or string) has an overhead of 16 bytes. I have actually seen posts intoning, “objects are expensive…” Just to be clear,

Objects are not expensive. Iterations are expensive, quadratic algorithms are expensive.

In evaluating an algorithm you need to see how many operations must be completed or the size and nature of the N. An N made of up strings is different than an N made up of Booleans or integers. A quadratic (N²) and cubic (N³) algorithm are among the worst. They’re gobbling up kilo- or megabytes, and so that 16 bytes seems pretty silly to worry about. So instead of seeing an algorithm weight expressed as N² + 84 bytes, you’ll just see it expressed as ~N². (When you see a ~ (tilde) in an algorithm, it denotes ‘approximately.’) Another way of understanding the ~ is to note, They left the bag of pennies.

Lesson 2: Watch out for Nested Loops; they’re Quadratic!

I’ve never liked nested loops, and while I admit that I’ve used them before, I just didn’t like them. They were hard to unwind and refactor, and they always seemed to put a hiccup in the run-time. Now I know why I don’t like them; they’re quadratic.

Quadratic algorithms have the following feature: When the N doubles, the running time increases fourfold.

An easy way to understand the problem with quadradics is to consider a simple matrix or table. Suppose you start with a table of 5 rows and 5 columns. You would create 5² cells—25 cells. Now if you double the number to 10, 10² cells = 100. That’s 4 x 25. Double that 10 to 20 and your have 20² or 400. A nested loop has that same quality as your N increases. If both your inner and outer loop N increases, you’re heading for a massive slowdown.

Algorithms, OOP and Design Patterns are Mutually Exclusive

An important fact to remember is that good algorithms do not guarantee good OOP. Likewise, good OOP does not mean good algorithms. Good algorithms make your code execute more efficiently and effectively. Good OOP makes your programs easier to reuse, update, share and change. Using them together is the ultimate goal of a great program.

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