Tag Archive for 'beginners php oop'

PHP Introduction to OOP: UI-Client-Request

clientBasicAn Easy Start

A lot of starting concepts in OOP seem designed to confuse and warn off developers who want to move up to OOP from sequential and procedural programming. This post is to give you a bit of what was presented at the NE PHP & UX Conference and to provide a simple yet clear introduction to OOP applied to PHP.

The easiest way (and least confusing) is to begin with the idea of “objects” and communication between objects. As you may know, objects are made up of classes containing “properties” and “methods.” Properties look a lot like PHP variables and methods like functions. So, think of properties as things a car has–like headlights, a steering wheel and bumpers, and think of actions your car can take, like turning left and right or going forward and reverse as methods.

The “blueprint” for an object is a class, and when a class is instantiated in a variable, it becomes an object. Objects communicate with one another by access to public properties and methods.

At the 2014 NE PHP & UX Conference in Boston, I told those at my session that I’d have some materials for them, and so you can download them here. One is a folder full of examples from my session and the other is an introductory book (in draft form) for getting started in OOP for PHP users. Also, the Play buttons runs the little example program for this post.
PlayconfFilesoopBook

A Request-Fulfill Model

At the heart of OOP is some system of communication. The simplest way to think about communication between objects is a request-fulfill model. A client makes a request to an object to get something. The request can originate in the user UI, and it is passed to a client who finds the correct class and method to fulfill the request. Figure 1 shows a file diagram with an overview of this model:

Figure 1: Object communication

Figure 1: Object communication

In Figure 1, you can see that the only non-object is the CSS file (request.css), and so in a way, you’re used to making requests for an external operation if you’ve used CSS files. However, CSS files are not objects but rather depositories. Likewise, external JavaScript (.js) files can be called from HTML documents for use with Web pages, but they too are not objects.

Encapsulating HTML in a Class

With PHP, the UI is handled by HTML, but that does not mean that it cannot be encapsulated in a PHP object. Encapsulation is not accomplished by simply adding a .php extension to the file name, but rather, fully wrapping the HTML in a PHP class. The easiest way to do that is with a heredoc string. The following example shows how a fully formed HTML5 document is encapsulated:

Listing #1:

< ?php
class RequestUI
{
    private $ui;
 
    public function request()
    {
        //Heredoc wrapper
        $this->ui=< <<UI
        <!DOCTYPE html>
<html>
<head>
    <link rel="stylesheet" type="text/css" href="request.css"/>
    <title>Request</title>
</head>
 
<body>
    <h3>Mathster Mind:<br /> The UI Class & Method Requester</h3>
<form name='require' action='Client.php' method='post' target='feedback'>
    <input type='hidden' name='class' value='MathsterMind'/>&nbsp;MathsterMind Class<br />
    <input type='text' name='num' size='6'/>&nbsp;Enter value <br />
 
    <fieldset>
        <legend>Methods</legend>
    <input type='radio' name='method' value='doSquare'/>&nbsp;Square the value<br />
    <input type='radio' name='method' value='doSquareRoot'/>&nbsp;Find the squareroot of the value<br />
    </fieldset><br />
    <input type='submit' name='send' value='Make Request'/>  
</form>
<iframe name='feedback'>Feedback</iframe>
 
</body>
</html>
UI;
    echo $this->ui;
    }  
}
//Instantiate an object from the class
$worker=new RequestUI;
//Call the public method from the instantiated object
$worker->request();
?>

The key aspect of encapsulating HTML in a class is the heredoc wrapper:

//Heredoc wrapper
$this->ui=<<<UI
//HTML Code
UI;

A heredoc string begins with three less-than symbols (they look like chevrons laid on their side), the name you give the heredoc string and it ends with heredoc string name fully on the left side of the source code and terminated with a semi-colon. Typically, the heredoc string is assigned to a variable ($this->ui). The great thing about using heredoc, is that you can develop and debug your HTML document, and once it’s all ready, you just paste it into a heredoc wrapper. Now, instead of a free range chicken running around with snippets of PHP code, you have a fully encapsulated object. Thus, your UI is a PHP class with all of the possibilities and security of a well formed class. (Click below to see how requests are “caught” by a PHP client.)
Continue reading ‘PHP Introduction to OOP: UI-Client-Request’

Share

PHP Recursion: The Fundamentals

recursionNailing Down Recursion

On more than one occasion on this blog, I’ve wandered off into the land of operations to examine recursion. In looking over past recursion posts and recursion discussions on the Web, I found a lot of bad information, partial information and helpful information. Likewise, I consulted some programming books, especially Robert Sedgewick’s and Kevin Wayne’s 2011 edition (4th) of Algorithms. Also, I found a great and detailed article on recursion by David Matuszek. Robert Sedgewick and Kevin Wayne are professors at Princeton and David Matuszek is a professor at the University of Pennsylvania. Not surprisingly, their focus is on larger conceptual and mathematical issues surrounding computer programming and the role that recursion plays in that context.

However, I also wanted to get a non-academic view from developers, and I found two very good posts on Martin Fowler’s Refactoring site by Dave Whipp and Ivan Mitrovic. For those of you not familiar with Martin Fowler, he’s written books and articles on computing and is one of the founders of the Agile Movement in program development. He is a primary consultant to businesses and institutions who want to optimize their programs for efficiency and effectiveness. Among PHP developers the Agile approach to programming is quite popular.

What is Recursion?

In a nutshell,

Recursion in computer programming occurs when a method calls itself.

While that definition is a starting point, a more detailed and useful one is provided by Sedewick and Wayne. They spell out three features in a good recursive method:

  1. A recursion begins with a conditional statement with a return. This is called the base case (or halting case), and it supplies the criterion which will stop the recursive operation.
  2. Recursive calls to sub-problems converge to the base case. Each call must bring the values in use closer to the halting conditions.
  3. Called sub-problems should not overlap.

You can find a lot of discussions and debate about the definition and use of recursive methods in programming, but the fundamental fact remains that recursion is one of the central ideas in computer science. As a professional programmer, you need to know about recursion and you should use it. This does not mean you have to use it all the time, but you need to understand what you can do with it and its limitations and advantages. Start off with the following implementations and download the code:
PlayDownload

In PHP and other computer programs, recursion and the need for it arise all the time. So you should have some sense of how to use it and when. Like other computing concepts, you may not use it all the time, but when you need it, you really need it.

World’s Easiest Recursive Function

To get started we’ll look at a simple recursive call. It is a version of what kids do when you take them on a trip. (And what you did when you were a kid on a trip…) You’d ask the reasonable question,

Are we there yet?

If you kept calling the same query as soon as you’d received a negative response, it has recursive-like qualities. The “No!” is the base case, and the car moving to the objective (“there”) is the change that occurs between each call to the query, “Are we there yet?”

//Recursion.php
< ?php
class Recursion
{
    private $ask="<span style='font-family:sans-serif;'>Are we there yet?<br />";
    private $answer="No!<br />";
    private $counter=0;
    public function __construct()
    {
        $this->thereYet();
    }
    private function thereYet()
    {
        //Base case (also called 'halting case')
        if($this->counter < =10)
        {
            echo $this->ask;
            echo $this->answer;
            $this->counter++;
            //Recursive call
            return $this->thereYet();
        }
        else
        {
            echo "<p></p>" . $this->ask;
            $this->answer="<strong><em>Yes! We are there!</em></strong>" ;
            echo $this->answer;
        }
    } 
}
?>

The return value calls for a recursive event inside the thereYet() method. With each call, the counter variable’s value moves toward convergence with the base case. After 10 calls, the counter variable exceeds the base case and no more self-calls are made by the thereYet() method.

While that example could be handled by iteration in a loop; it provides another way to accomplish a task. It’s easy to understand and meets the criteria set up for recursion. (Click below to see more.)
Continue reading ‘PHP Recursion: The Fundamentals’

Share

PHP OOP: Encapsulating & Communicating with JavaScript and HTML5

EncapDocCan We Talk?

The initial discussion of the Memento design pattern illustrated how a state could be saved in a different object than the one in which the state originated. A Caretaker object holds the saved state and when requested, it returns the state to the Originator, all without breaking encapsulation. A practical example of employing the Memento that comes to mind is where the user is looking through a list. As she goes through the list, she sees different items (flowers in this case) that she is considering. However, because it’s a long list, she cannot remember which one she likes; so she tags those she is considering. After going through the whole list (all of the different flowers), she can easily recall those that she had tagged–recall them from a Memento. Play the little app and download the source code before going further:
PlayDownload

Communicating with HTML and JavaScript

Working HTML and JavaScript into PHP is no great shakes, and most PHP developers probably have done so at one time or another. However, most of the time I find myself creating horrible mixes of code for a one-off use with nothing encapsulated. The goal here is to see how everything in the application can be encapsulated and at the same time communicate. The purpose here is to find a single state variable that is used by HTML, JavaScript and PHP. Further, that state must be available for placing into a Memento object and stored for later use. (This post simply examines one way to encapsulate everything and have them communicate; however, material from this post will be used in developing a Memento example in a future post.) Also, I wanted to import all of the JavaScript and CSS separately. Figure 1 shows the general plan. (The ‘gardner’ folder contains the flower JPEG images.)

Figure 1: Encapsulating JavaScript, CSS and HTML into EncapDoc PHP class

Figure 1: Encapsulating JavaScript, CSS and HTML into EncapDoc PHP class

The CSS is just the stylesheet and it contained no functionality that you often find when it is used in conjunction with jQuery. I needed the JavaScript for clicking through the images. Had I swapped images using PHP I’d probably have to reload an HTML page with every swap and that seem prohibitively expensive. So I wrote the most simple JavaScript swap program I could think of with two functions for swapping and an added JavaScript function to get the initial starting picture (an integer value) passed from PHP. The following JavaScript listings shows how simple the script is:
Continue reading ‘PHP OOP: Encapsulating & Communicating with JavaScript and HTML5’

Share

PHP OOP: Back to Basics

beginBack to Basics

Whenever I venture outside of PHP, which has become more regular as I’m working on app development in both iOS and Android. The former is Objective C and the latter, Java. Both languages are embedded in OOP and design patterns. It is during these ventures abroad (so to speak) that I’m reminded of some core issues in good OOP. I usually notice them when I realize that I’m not exactly paying attention to them myself.

Don’t Have the Constructor Function Do Any Real Work

When I first came across the admonition not to have the constructor function do any real work, I was reading Miško Hevery’s article on a testability flaw due to having the constructor doing real work. More recently, I was reviewing some materials in the second edition of Head First Java, where the user is encouraged to,

Quick! Get out of main!

For some Java and lots of C programmers “main” is the name for a constructor function, but I like PHP’s __construct() function as the preferred name since it is pretty self-describing. “Main” is a terrible name because the real main is in the program made up of interacting classes.

In both cases, the warning about minimizing the work of the constructor function is to focus on true object oriented applications where you need objects talking to one another. Think of this as a series of requests where a group of people are all cooperatively working together, each from a separate (encapsulated) cubicle, to accomplish a task. By having the constructor function do very little, you’re forcing yourself (as a programmer) to use collaborative classes. Play the example and download the code to get started:
PlayDownload

A General Model for PHP OOP

As a nice simple starting place for PHP OOP, I’ve borrowed from the ASP.NET/C# relationship. ASP.NET provides the forms and UI, and C# is the engine. As an OOP jump-off point, we can substitute HTML for ASP.NET and PHP for C#. The Client class is the “requester” class. The UI (HTML) sends a request to the Client, and the Client farms out the request to the appropriate class. Figure 2 shows this simple relationship.

Figure 1: A Simple OOP PHP Model

Figure 1: A Simple OOP PHP Model

If you stop and think about it, OOP is simply a way to divide up a request into different specializations.

Avoid Conditional Statements if Possible

Figure 2: Requests begins with a UI built in HTML

Figure 2: Requests begins with a UI built in HTML

If you avoid conditional statements, and this includes switch statements, I think you can become a lot better programmer. In the example I built for this post, the user chooses from two different types of requests (classes), and each request has a refined request (method) that provides either of two different kinds of math calculations or display options. Figure 2 shows the UI (HTML) for the example. If the user selects “Do a Calculation” it sends the request to the Calculate class, but if the user selects “Display a story”, the request is handled by the Display class. Further, not only must the right class be selected, the right method in that class must be selected as well. The obvious answer is to get information from the UI and using a switch or set of conditional statements work out in the Client how to handle each request. You could even use (shudder) nested conditional statements. That approach could work, but when you start piling up conditional statements, you’re more likely to introduce errors, and when you make changes, you’re even more likely to make errors. The only good thing about conditionals is that you don’t have to tax your brain to use them.

Suppose for a second that all of your conditional statements were taken away. How, using the information sent from the HTML UI to the Client class can the selections be made without conditional statements? (Think about this for a moment.)

Think, pensez, pense, думайте, piense, 생각하십시오, denken Sie, 考えなさい, pensi, 认为, σκεφτείτε, , denk

Like all things that seem complex, the solution is pretty simple. (Aren’t they all once you know the answer.) Both classes were given the value of their class name in their respective radio button input tags. Likewise, the methods were given the value of their method names. With two radio button sets (request and method), only two values would be passed to the Client class. So all the Client had to do was to use the request string as a class name to instantiate an instance of the class, and employ the following built-in function:

call_user_func(array(object, method));

That generates a request like the following:

$myObject->myMethod;

In other words, it acts just like any other request for a class method. By coordinating the Client with the HTML UI, that was possible without using a single conditional statement. In this next section, we’ll now look at the code.
Continue reading ‘PHP OOP: Back to Basics’

Share

PHP Game Coding: SVG Movement

flashEncapsulating Movement

Any sane person would abandon PHP for JavaScript, Ajax, jQuery or some other client-side language that would work directly with Web-based SVG graphic elements and attributes. In doing so, though, it would give up on both the OOP capacity of PHP (lacking in these other languages) and low cost (no open socket server) inter-internet games (i.e., remote multiplayer games.)

Ironically (for some), the easiest part of creating action games is the game physics. You just need to take a formula from physics (e.g., deceleration, acceleration) and turn it into an algorithm. Eventually, we’ll get to that luxury, but first we need to work out the mechanics of changing the position of a SVG graphic on a grid. Before getting into that discussion, click the Play button to see the end results (goal) and the Download button to see the code:
PlayDownload

As you will see, there’s not a lot to play with, but it does deal with two velocity issues; velocity itself and capacity. It’s like comparing the velocity of a 2014 Rolls-Royce Wraith with that of a 1988 Trabant 601. Both cars can attain speeds of 100 km/hr (62 mph), but the Wraith can do it much faster and go far above that speed because it has a more powerful engine. It has greater capacity.

The Space Grid

In the previous post on using SVG graphics in making games, you can see the grid setup, and in that grid you can determine distance and collision using simple geometry. If you’ve spend any time with SVG graphics, you will find a animation system to move graphics along paths. The problem with that system (for now at least) is working out position and collision detection. Movement along paths has grid-like parameters in defining X and Y locations on a grid, but paths can also be defined in terms of curves, and knowing the position of an object at any given time can be problematic. Further, movement is a function of timing using the SVG animateMotion element. For example, consider the following path:

    animateMotion fill=”freeze” path=”M 0 0 L 100 150″ dur=”.5s”

It moves an SVG object from 0,0 to 100,150 in a half a second (0.5 seconds). There is no checking along the way for collision. Using a Bézier curve the following movement goes from 0,0 to 300,0 in two seconds (2s) but it curves downward before reaching its destination.

    animateMotion fill=”freeze” path=”M 0 0 T 100 150 T 300 0″ dur=”2s”

Again, what it may have collided with is unknown given both the timing of the motion and the curve. This is not to say that every point could not somehow be tracked, but at this point I’d rather take a more familiar route to movement and collision detection.

Moving SVG objects involves changing their X and Y values. I’m calling the frequency with which the X and Y values are updated, “capacity” and the amount of change “velocity.” Rather than using the animateMotion SVG element, this example changes the object’s X value through timed updates and variable values in the number of pixels each timed update generates. For example, an update of every 50 milliseconds is faster than one of every 100 milliseconds—there’s less time between each update pause. Likewise, an X increment of 10 pixels will cause faster movement than an update of 5 pixels.

A timed loop fires a function that changes the ship’s position:

?View Code JAVASCRIPT
function moveShip()
{
     // Change the ship's position
     shipX += $this->velocity;
     shipX = shipX % 500;
     oopz.setAttribute("x", shipX);
}

As you can see the code is JavaScript using a PHP variable ($this->velocity) to set the speed. I would have preferred to do it using all PHP, but needed to use the JavaScript setAttribute method for moving the ship’s X position without having to create a new object. Changing the speed using capacity (loop timing) and velocity (amount of variable increment) requires PHP to create another SVG object, and for demonstration purposes, that’s fine. In an action game, though, it’d eat up a lot of resources.

The “ship” (rectangle) only moves from left to right at this time, and when it leaves “the galaxy” it loops around and comes in the other end. Using the modulus of 500 (% 500), the value will always be calculated correctly when moving from left to right (in both JavaScript and PHP); however, moving from right to left, as soon as the X position is 0, it fails. (See this post on game algorithms for a detailed explanation and comparison of how the modulus operator works differently in Python than PHP and JavaScript). It’s an easy fix using conditional statements, but that’s so…I don’t know…inelegant? See what you can do. For now, continue on to see how the Move class is created and used.
Continue reading ‘PHP Game Coding: SVG Movement’

Share