Object Oriented Programming

Radon3k

I'm very hung up on OOP. I can't seem to grasp the concept of classes, objects, methods, functions, etc. I don't understand when or where to use it. Is there any one place that has a clear explanation of how all of this works or could someone perhaps explain it to me? I have a few PHP books and I've read over the chapters on the OOP parts and I'm still not getting it. I picked up on everything else just fine, but OOP has really got me stuck. Any help would be greatly appreciated. Thanks! 🙂

sgoku01

OOP is used for stucturing your code.
Here's an example:
This is your info-class with all the info:

class information {

var $sentence_1 = "";
var $version = "v1.0.1-beta";
var $testing = "";

$test_to_set = "hello";

if ( empty($testing) )
{
$this->make_test();
}

function make_test() {
$this->testing = $this->test_to_set;
}

function make_sentence_1( $thing ) {
$this->sentence = $thing;
}

} // END CLASS

This is a random code:

$info = new information();

// This will print the version
// - this will be v1.0.1-beta
echo $info->version;

// This will print our test-variable
// - this will be hello
echo $info->testing;

// This will print our sentence
// - this will be an empty string
echo $info->sentence_1;

// Now we will run a function
$info->make_sentence( 'blah' );

// And we print the sentence again
// - now it will be blah
echo $info->sentence_1;

// This will probable give an error:
echo $info->test_to_set;

You only use it for structuring your code. It has no magical functions or something.
When you have a code and you want to 'include' a class, you type: $var = new class_name();
Every time you want a variable or run a function, you type $var-> and you set wich variable you want of wich function you want to run. (like I have done in the 'random code')

I hope you understand now? If you have questions, pm me 🙂

Radon3k

Erm, I'm sorry but I really don't follow that. I read the code several times and picked up kind of what it did but don't understand why you did it.

martyn

I do not get this bit:

function make_sentence_1( $thing ) {
$this->sentence = $thing;
}

AND

echo $info->sentence_1;

Should it not be:

function make_sentence_1( $thing ) {
$this->sentence_1 = $thing;
}

Norman_Graham

I've been struggling to understand what OOP actually is for a little while now. I think the first step is to understand what is meant by the word 'object'. An object is a thing like a table or a violin, but not an albatross since objects are generally accepted as being inanimate. This is what the word object means in English.

In Cyberia, an object ain't much different. An object can be a window, a document, a frame, a flash film, a form etc. It is a thing upon which a code set can operate. Javascript routines of the type SetNewWindow() or whatever (I know that's not real Javascript) are operating on the window object. PHP routines that create dynamic news reports are operating on the document object (and possibly also on the form, frame and window objects). OOP is a way of constructing your code such that it addresses a particular object level: browser, window, frame, document, form etc (and more or less in that order).

That's as far as I've got at the moment, but it has been a big step forward for me, and I made this quantum leap by looking at a single page of O'Reilly's Javascript tome on which there is a diagram of level 0 of the DOM (document object model). Up till that point, the word 'object' in OOP had had no meaning for me.

I'll wait now for all the replies telling me that I've misunderstood the concept. And perhaps a couple of replies which will lead me on to a better understanding of what OOP is?

Norman

ednark

maybe this explaination will help..

You have to write the same piece of info several time in a program, say a username. Instead of hard coding it you place it in a vairable called $username, an call that variable each time you want to use it.

if you write the same piece of logic over and over again (the same few lines of code) you would remove those lines, place them in a function, and call that function in place of that code.

if you have a group of functions you call over and over again. and if they act on the same kind of data each time, say and array with specific keys. You can take that block of functions and data, and place them into an object.

Objects are not necessary, they are just one method of making certain procedures more easly accomplished. They can replicate copies of themselves.

its too complicated to explain all the situations where objects are helpful, and anything an object can do can be replicated with just functions.

its supposed to make your life easier like here is a sample object

here is a situation where i want to get user 12 from the database and print his name, change it, and store it back in the database

$user = new User();
$user->getFromDatabase( 'id', 12 );
print $user->name;
$user->name = 'ednark';
$user->storeInDatabase();

but here is what it looks like using arrays and functions

$user = array();
$user = getFromDatabase( 'id', 12 );
print $user['name'];
$user['name'] = 'ednark';
storeInDatabase( $user );

so as you can see

in objects the functions and data are tied to the object
with functions... they are seperate.. and you have to just use them correctly together...

planetsim

There is no real good explanation of OOP. You must try and comprehend it. The best way to do that is by an example.

The best example and the way i learnt was by making a MySQL Class

a MySQL Class could consist of these functions; connect, select, query, error, fetch_array, numrows etc etc..

The list can go on.

So why keep connecting or creating 10 queryies which all connect to the db then fetch the data when we can use one file that does that or in our case a file that has the class

Ok lets explain some basic OOP

class MySQL{

}

thats how you create a class
calling the class can be like so

$class = new class;

or in our case

$class = new MySQL;

from there we can have a function in that class so

class MySQL{

function Connect()
{
}
}

to get the class then get the function we can do this..

$class = new MySQL;
$class->Connect();

$class turned into the object.

$class->Connect(); can been seen something like this...

$this->Connect();

That can only be used if your actually in the object itself..

all that is there is object->function but can be object->variable

Hope that helps just a little in the basics

matto

try this approach. first, in order to avoid confusion about terms:

an "object" can be an object type (= a construction plan for an object which we call class). when we program OO, we write classes. Imagine a class "Client" which is designed to hold a client's info: first name, last name, age, ... and perform specific operations on it.
an "instantiated" object: i.e., an area in your computer's (php: the web server's) memory where the representation of something real (e.g. one specific client: John Doe, 42 years old) is stored at runtime. this representation has been built from a plan: the class.

Norman confused two things: 1. the object model of javascript is just one aspect of OO and does not help very much understanding OO principles for PHP programming.
2. an albatross can be an object (means: a class), too. Because more than one albatrosses exist. What is not senseful, is that you have a class JohnDoe42Years. A class is meant to be the construction plan of similar objects. We assume John Doe (42) is in fact only one single person. So it it useless to write a class for instantiating multimpe John Does (42).

most basic classes store information about a thing/person and allow to set/retrieve this information.

this means, a class consists of (a) attributes (= variables) and (b) methods (= functions).

our class "Client" has the attributes firstname, lastname, age
and (say) the methods: calculatebirthyear() and introduceyourself().

calculatebirthyear() should do a calculation and return the birthyear.
introduceyourself() returns a string "hello, I am [...] and I am [...] years old".

so far it's quite lame. the power of OO reveals itself when you start with INHERITANCE.

now imagine a class Vehicle (attributes: fabrication date, number_of_wheels, color)
then we need two more classes for our project which are based upon Vehicle: Truck and Bicycle.

you can say: "a Truck IS A Vehicle". thus, you can inherit it from Vehicle. It has all the Vehicle's attributes and methods PLUS some specific ones in addition. only these have to be written when you code your Truck class. say: Max_load and Has_Twin_Tyres or whatever.

each Vehicle-inheritaded class has a method getDescription() which prints out relevant attributes.

then, you can create a class ParkingLot. this is a COLLECTION class. it is meant to hold vehicle-type objects.

its most important attribute is an array: vehicles. furthermore, it has a method add_vehicle() which expects one instantiated Truck or Bicycle as a parameter.

Now a method getVehicleList() could be useful. the ParkingLot object can generate it by looping through the vehicles array and collecting each one's getDescription() information.

hope you get an impression of how objects can be used and how useful they can be. but note that design is everything with oo! search the web for oo tutorials. even in phpbuilder->articles there are useful introductions.

Radon3k

Thanks for the replies. I've read through them and for the most part they all make sense. Now that I have an understanding of what each of them does, I'm just having a hard time understanding when to use them. In one of the replies earlier someone said that there were too many instances to list. With that being said, do people who program in OOP generally pre-plan when and where they'll use OOP aspects or do they code then go back and clean it up?

Norman_Graham

Yo, Matto! Good job! I've read your explanation and I believe I understand it ... and I'm starting to see how this could be useful.

Thank you very much

Norman

BuzzLY

Originally posted by Radon3k
Thanks for the replies. I've read through them and for the most part they all make sense. Now that I have an understanding of what each of them does, I'm just having a hard time understanding when to use them. In one of the replies earlier someone said that there were too many instances to list. With that being said, do people who program in OOP generally pre-plan when and where they'll use OOP aspects or do they code then go back and clean it up?

Generally, if you are creating a small website that collects a bit of data and displays information, you probably won't use objects. Objects require a bit more planning, and probably wouldn't be worth the time.

However, if you are creating a complete application, let's say for instance a Bulletin Board application (like PHP-B😎, then you want to seriously look at what parts of your application can be reused over and over. That requires much planning, and in the long run can save you a lot of hassle and time.

Creating objects is a lot like creating a new programming language, or at least extending the language you are already using. It requires a lot of planning, and is not worth the effort if the project is not very big.

That said, most programmers know that it's almost impossible to plan for everything. Most of the time, you will write some snippet of code, then realize later that you have used that same code snippet 14 times. It would probably make a good class -- so you code it as a class and go back through your code to use it. If you are organized and document your work well, this isn't too difficult. If you are not that organized... well, how many of us have had to go back through all of our code to make global changes?

LOTS of fun!!!