Въведение
The PHYSICS OF THE SYSTEM
You cannot take the PHYSICS out of any SYSTEM (or environment) -- man-made OR natural. In every system, there lies the laws of physics (the laws of nature). For example, a moving object -- in a natural environment OR in a lab -- is always subject to the same forces that exist anywhere. Even a computer program has an environment, for example:
<?php
?>
Even though it had a very short life, it had an ENVIRONMENT which had POTENTIAL TO DO WORK, which made it a good candidate for a useful SYSTEM. If we think about a 3-Dimensional space as an environment, it is easy to imagine putting 'things' or 'objects' in that space AND doing things to them.
In the next invocation of PHP below, I am going to:
1. Create a 3-Dimensional space or ENVIRONMENT -- just by using the '<?php' tag.
2. Define the SYSTEM we want to use -- laws, rules, policies, structure, properties etc. -- with valid PHP class definitions.
3. Instantiate objects with the 'new' operator so we can poke it for a while.
4. Output some data to see if they obey the rules we wrote.
5. Here we go!
<?php
// 1. check, ENVIRONMENT created.
class Wheel
{
public $cir = 3.0; // circumference in feet.
public $rpm = 0.0; // rotations (spins) per minute.
public function __toString()
{
return 'Wheel [' .
'cir=' . number_format($this->cir, 2) . ' ft, ' .
'rpm=' . $this->rpm .
']';
}
}
// Wheel defined...
class Speedometer
{
public $wheel;
public function __construct(Wheel $wheel)
{
$this->wheel = $wheel;
}
public function getSpeed()
{
$speed = 0.0;
$wheel = $this->wheel;
if($wheel->rpm != 0.0)
{
$fpm = $wheel->cir * $wheel->rpm; // feet per minute
$fph = $fpm * 60; // feet per hour
$speed = $fph / 5280; // MPH = $fph / feet per mile
}
return $speed;
}
public function __toString()
{
return 'Speedometer [' .
'speed=' . number_format($this->getSpeed(), 2) . ' MPH, ' .
'wheel=' . $this->wheel .
']';
}
}
// Speedometer defined.
// 2. check, SYSTEM created.
$wheel = new Wheel();
$speedometer = new Speedometer($wheel);
// 3. check, Objects instantiated.
while($wheel->rpm <= 1500)
{
echo $speedometer . "<br>\n";
$wheel->rpm += 100;
}
// 4. check, data outputted.
?>
Speedometer [speed=0.00 MPH, wheel=Wheel [cir=3.00 ft, rpm=0]]
Speedometer [speed=3.41 MPH, wheel=Wheel [cir=3.00 ft, rpm=100]]
Speedometer [speed=6.82 MPH, wheel=Wheel [cir=3.00 ft, rpm=200]]
... etc ...
... etc ...
Speedometer [speed=51.14 MPH, wheel=Wheel [cir=3.00 ft, rpm=1500]]
5. check, there it went.
Основите
class
Всяка дефиниция на клас започва с ключовата дума class, последвана от името на класа, което може да бъде всяко име, което не е запазена дума в PHP. Следват чифт фигурни скоби, между които се поставя дефиницията на свойствата и методите на класа. Псевдо-променливата $this е налична, когато се извиква дадено свойство или метод от тялото на класа. $this представлява референция към извикания обект (обикновено обекта, на който принадлежи метода, но може да бъде и друг обект, ако методът се извиква статично в контекста на вторичния обект). Това е илюстрирано в следните примери:
<?php
class A
{
function foo()
{
if (isset($this)) {
echo '$this е дефинирана (';
echo get_class($this);
echo ")\n";
} else {
echo "\$this не е дефинирана.\n";
}
}
}
class B
{
function bar()
{
A::foo();
}
}
$a = new A();
$a->foo();
A::foo();
$b = new B();
$b->bar();
B::bar();
?>
Примерът по-горе ще изведе:
$this е дефинирана (a) $this не е дефинирана. $this е дефинирана (b) $this не е дефинирана.
Example #1 Проста дефиниция на клас
<?php
class SimpleClass
{
// дефиниция на свойство
public $var = 'стойност по подразбиране';
// дефиниция на метод
public function displayVar() {
echo $this->var;
}
}
?>
Стойността по подразбиране трябва да е константен израз, не (примерно) променлива, метод на клас или извикване на функция.
Example #2 Стойност по подразбиране за член на клас
<?php
class SimpleClass
{
// невалидни декларации на членове:
public $var1 = 'hello '.'world';
public $var2 = <<<EOD
hello world
EOD;
public $var3 = 1+2;
public $var4 = self::myStaticMethod();
public $var5 = $myVar;
// валидни декларации на членове:
public $var6 = myConstant;
public $var7 = self::classConstant;
public $var8 = array(true, false);
}
?>
Забележка: Разработени са много удобни функции за работа с класове и обекти. Можете да ги видите в глава Функции за класове и обекти.
За разлика от heredoc, nowdoc може да се използва в контекста на всякакви статични данни.
Example #3 Пример със статични данни
<?php
class foo {
// От PHP 5.3.0
public $bar = <<<'EOT'
bar
EOT;
}
?>
Забележка: Поддръжката на nowdoc е добавена в PHP 5.3.0.
new
За да бъде създадена инстанция на клас, трябва да се създаде нов обект и да се присвои на променлива. Когато се създава обект, той винаги ще бъде присвоен на променливата, освен ако няма конструктор, който да хвърля изключение при грешка. Класовете трябва да бъдат дефинирани преди инстанцииране (а в някои случаи това е задължително).
Example #4 Създаване на инстанция
<?php
$instance = new SimpleClass();
?>
В контекста на клас може да се създаде нов обект посредством new self и new parent.
Когато се присвоява вече създадена инстанция на клас към нова променлива, новата променлива ще има достъп до същата инстанция като присвоения обект. Нещата стоят по същия начин и когато се предават инстанции към функции. Копие на вече създаден обект може да се създаде чрез клониране.
Example #5 Присвояване на обект
<?php
$assigned = $instance;
$reference =& $instance;
$instance->var = '$assigned ще приеме тази стойност';
$instance = null; // $instance и $reference приемат стойност null
var_dump($instance);
var_dump($reference);
var_dump($assigned);
?>
Примерът по-горе ще изведе:
NULL
NULL
object(SimpleClass)#1 (1) {
["var"]=>
string(30) "$assigned ще приеме тази стойност"
}
extends
Даден клас може да наследи свойства и методи от друг клас, чрез използването на ключовата дума extends. Не се поддържа множествено наследяване, т.е. даден клас може да има само един базов клас.
Всички наследени свойства и методи могат да бъдат дефинирани отново, чрез повторното им дефиниране със същото име, с което са били дефинирани в родителския клас. Изключение се явяват случаите, когато в родителския клас даден метод е дефиниран като final. Достъпът до повторно дефинираните свойства или до статичните методи на родителския клас се осъществява чрез ключовата дума parent::
Example #6 Просто наследяване на клас
<?php
class ExtendClass extends SimpleClass
{
// Повторно дефиниране на родителския метод
function displayVar()
{
echo "Наследяване на клас\n";
parent::displayVar();
}
}
$extended = new ExtendClass();
$extended->displayVar();
?>
Примерът по-горе ще изведе:
Наследяване на клас стойност по подразбиране
add a note
User Contributed Notes
Основите
Jeffrey
21-May-2012 10:36
Manish Gupta
22-Oct-2011 10:07
Some thing that may be obvious to the seasoned PHP programmer, but may surprise someone coming over from C++:
<?php
class Foo
{
$bar = 'Hi There';
public function Print(){
echo $bar;
}
}
?>
Gives an error saying Print used undefined variable. One has to explicitly use (notice the use of <?php $this->bar ?>):
<?php
class Foo
{
$bar = 'Hi There';
public function Print(){
echo this->$bar;
}
}
?>
<?php echo $this->bar; ?> refers to the class member, while using $bar means using an uninitialized variable in the local context of the member function.
Marcus
05-Feb-2011 11:00
Here's another simple example.
<?php
// PHP 5
// class definition
class Bear {
// define properties
public $name;
public $weight;
public $age;
public $sex;
public $colour;
// constructor
public function __construct() {
$this->age = 0;
$this->weight = 100;
}
// define methods
public function eat($units) {
echo $this->name." is eating ".$units." units of food... ";
$this->weight += $units;
}
public function run() {
echo $this->name." is running... ";
}
public function kill() {
echo $this->name." is killing prey... ";
}
public function sleep() {
echo $this->name." is sleeping... ";
}
}
// extended class definition
class PolarBear extends Bear {
// constructor
public function __construct() {
parent::__construct();
$this->colour = "white";
$this->weight = 600;
}
// define methods
public function swim() {
echo $this->name." is swimming... ";
}
}
?>
Doug
07-Oct-2010 07:29
What is the difference between $this and self ?
Inside a class definition, $this refers to the current object, while self refers to the current class.
It is necessary to refer to a class element using self ,
and refer to an object element using $this .
Note also how an object variable must be preceded by a keyword in its definition.
The following example illustrates a few cases:
<?php
class Classy {
const STAT = 'S' ; // no dollar sign for constants (they are always static)
static $stat = 'Static' ;
public $publ = 'Public' ;
private $priv = 'Private' ;
protected $prot = 'Protected' ;
function __construct( ){ }
public function showMe( ){
print '<br> self::STAT: ' . self::STAT ; // refer to a (static) constant like this
print '<br> self::$stat: ' . self::$stat ; // static variable
print '<br>$this->stat: ' . $this->stat ; // legal, but not what you might think: empty result
print '<br>$this->publ: ' . $this->publ ; // refer to an object variable like this
print '<br>' ;
}
}
$me = new Classy( ) ;
$me->showMe( ) ;
/* Produces this output:
self::STAT: S
self::$stat: Static
$this->stat:
$this->publ: Public
*/
?>
ben dot corne at gmail dot com
26-Apr-2010 12:35
method calling context aware. By this I mean it will get treated differently while being in a new statement compared to being in a regular call.
Example:
<?php
class Foo {
private $className = 'Bar';
public function make() {
return new $this->className();
}
public function callClassName() {
$this->className();
}
public function className() {
echo "foo\n";
}
};
class Bar {
public function hello() {
echo "bar\n";
}
};
$foo = new Foo();
$bar = $foo->make();
echo "expecting 'bar': ";
$bar->hello();
echo "expecting 'foo': ";
$foo->callClassName();
?>
even tough $this->className() is written two times in exactly the same way, the one contained in a new statement gets the className field and the other performs the actual method.
Anonymous
06-Nov-2009 06:54
It is also simple to get or set a property with a name determined at runtime:
<?php
$e=new E();
$e->{"foo"} = 1; // using a runtime name
// is the same as doing:
// $e->foo = 1;
?>
moty66 at gmail dot com
16-Aug-2009 07:59
I hope that this will help to understand how to work with static variables inside a class
<?php
class a {
public static $foo = 'I am foo';
public $bar = 'I am bar';
public static function getFoo() { echo self::$foo; }
public static function setFoo() { self::$foo = 'I am a new foo'; }
public function getBar() { echo $this->bar; }
}
$ob = new a();
a::getFoo(); // output: I am foo
$ob->getFoo(); // output: I am foo
//a::getBar(); // fatal error: using $this not in object context
$ob->getBar(); // output: I am bar
// If you keep $bar non static this will work
// but if bar was static, then var_dump($this->bar) will output null
// unset($ob);
a::setFoo(); // The same effect as if you called $ob->setFoo(); because $foo is static
$ob = new a(); // This will have no effects on $foo
$ob->getFoo(); // output: I am a new foo
?>
Regards
Motaz Abuthiab
alex c
07-Aug-2009 12:17
ok this really basic but I always forget this. I always get an error like:
Fatal error: Call to a member function on a non-object
when i deal with oops
if it were me finding the error i'd search the internet for hours and then it would occur to me, I'm putting my class operator inside a function, but i would define the class in global file.
so like this:
test.php
<?
include(class.php);
$class = new newclassname;
function function1(){
$class->dofunc();
}
?>
you'll get some die errors and try and do this with function1,
function function1(){
newclassname::dofunc();
}
but if you're using $this inside your class then you'll get another error on non object
so basically, all you need to do is:
function function1(){
$class = new newclassname;
$class->dofunc();
}
or
function function1(){
global $class;
$class->dofunc();
}
i know it's simple, but it always gets me!
the_french_cow at hotmail dot com
14-Jul-2009 06:54
For those of us who are new to inheritance, private functions are not visible in an inherited class. Consider:
<?php
class A {
protected function func1() {
echo("I'm func1 in A!<br/>");
}
private function func2() {
echo("I'm func2 in A!<br/>");
}
}
class B extends A {
public function func3() {
echo("I'm func3 in B!<br/>");
$this->func1();
$this->func2(); // Call to private function from extended class results in a fatal error
}
}
$b = new B;
$b->func3(); // Ends in a fatal error
// OR
$b->func1(); // Call to protected function from outside world results in a fatal error
?>
If you want a function to be accessible in class B but not to the outside world, it must be declared as protected.
Notes on stdClass
09-Jul-2009 03:26
stdClass is the default PHP object. stdClass has no properties, methods or parent. It does not support magic methods, and implements no interfaces.
When you cast a scalar or array as Object, you get an instance of stdClass. You can use stdClass whenever you need a generic object instance.
<?php
// ways of creating stdClass instances
$x = new stdClass;
$y = (object) null; // same as above
$z = (object) 'a'; // creates property 'scalar' = 'a'
$a = (object) array('property1' => 1, 'property2' => 'b');
?>
stdClass is NOT a base class! PHP classes do not automatically inherit from any class. All classes are standalone, unless they explicitly extend another class. PHP differs from many object-oriented languages in this respect.
<?php
// CTest does not derive from stdClass
class CTest {
public $property1;
}
$t = new CTest;
var_dump($t instanceof stdClass); // false
var_dump(is_subclass_of($t, 'stdClass')); // false
echo get_class($t) . "\n"; // 'CTest'
echo get_parent_class($t) . "\n"; // false (no parent)
?>
You cannot define a class named 'stdClass' in your code. That name is already used by the system. You can define a class named 'Object'.
You could define a class that extends stdClass, but you would get no benefit, as stdClass does nothing.
(tested on PHP 5.2.8)
webmaster at oehoeboeroe dot nl
03-May-2009 05:03
If you pass $this by reference and then assign a new value to it, it will not behave as you might expect as illustrated by this example:
<?php
class TestClass
{
public $data;
function setData(&$data) {
$this->data =& $data;
}
function hasData(&$data) {
$saved = $data;
$data = true;
$result = $this->data === true;
$data = $saved;
return $result;
}
function isDataOf(&$object) {
return $object->hasData($this);
}
}
$o1 = new TestClass;
$o2 = new TestClass;
$o1->setData($o2);
$o2->setData($o1);
var_dump($o1->hasData($o2)); // true as expected
var_dump($o2->hasData($o1)); // true as expected
var_dump($o1->isDataOf($o2)); // false even though $o1 is in fact the data of $o2
var_dump($o2->isDataOf($o1)); // false even though $o2 is in fact the data of $o1
?>
You can make this example work by replacing the hasData method with:
<?php
function hasData(&$data) {
return $data === $this->data;
}
?>
However, although I've not tested this, I've been told that Zend Engine 1, i.e. PHP 4, will choke on the === parameter when comparing recursing objects.
ialsoagree
23-Apr-2009 08:03
Unfortunately, Arpit's solution creates a new class and leaves the old class inaccessible. If you need access to members of the class you are in you'll be unable to get such access. This can be a huge problem.
However, there is a solution:
<?php
class MyClass {
public $message = 'Hello';
public function MyClassFunction() {
function innerFunction(&$this_thing, $message = null) {
$this_thing->message = (!is_null($message)) ? $message : $this_thing->message;
$this_thing->echo_something();
}
innerFunction($this); // echoes 'Hello'
innerFunction($this, '<br/>New Message'); // echoes '<br/>New Message'
}
public function echo_something() {
echo $this->message;
}
}
$class = new MyClass;
$class->MyClassFunction();
?>
By passing $this as a variable by reference, you can access members of the class and even update them. If you don't want to be able to update them, you can simply pass $this to the function but not as a reference.
Arpit
06-Feb-2009 06:14
//try this code if you define a new class inside an object method than we can refer to "$class->message"
//unset this instance doesn't affected the previous one
//it will not report a fatal error
<?php
class MyClass {
public $message = 'Hello';
public function MyClassFunction() {
function InnerFunction() {
$class = new MyClass;
print_r($class);
echo $class->message;
unset($class);//unset this doesn't affected the previous one or we can also use different name $classNew=new MyClass;
}
innerFunction();
}
}
$class = new MyClass;
$class->MyClassFunction();
?>
ialsoagree
02-Feb-2009 04:23
I think it's worth mentioning that if you define a function inside of an object method, that function cannot refer to "$this" - doing so will result in PHP reporting a fatal error:
Fatal error: Using $this when not in object context
<?php
class MyClass {
public $message = 'Hello';
public function MyClassFunction() {
function InnerFunction() {
echo $this->message; // Reports a fatal error
}
innerFunction();
}
}
$class = new MyClass;
$class->MyClassFunction();
?>
This issue cannot be solved by using the Scope Resolution Operator if you're trying to access a variable:
<?php
class MyClass {
public $message = 'Hello';
public function MyClassFunction() {
function InnerFunction() {
echo MyClass::message; // Reports a fatal error
}
innerFunction();
}
}
$class = new MyClass;
$class->MyClassFunction();
?>
Additionally, you can NOT create a public function to access that variable:
<?php
class MyClass {
public $message = 'Hello';
public function MyClassFunction() {
function InnerFunction() {
MyClass::echoSomething();
}
innerFunction();
}
public function echoSomething() {
echo $this->message; // Reports a fatal error
}
}
$class = new MyClass;
$class->MyClassFunction();
?>
Note that in this last case, the error is generated on the line below echoSomething function declaration, not at MyClass::echoSomething();
However, it is worth noting that when called directly, echoSomething works fine:
<?php
class MyClass {
public $message = 'Hello';
public function MyClassFunction() {
function InnerFunction() {
MyClass::echoSomething();
}
innerFunction();
}
public function echoSomething() {
echo $this->message; // Echoes 'Hello'
}
}
$class = new MyClass;
$class->echoSomething();
?>
hugo (@) apres (dot) net
16-Jan-2009 08:37
A simple approach to Multiple Inheritance
You can give yourself something approaching multiple inheritance with the following class:
<?php
class inheritance{
var $bases = array();
static function error_die( $errno, $errstr, $errfile, $errline ) {
$backtrace = debug_backtrace();
$detail = $backtrace[4];
var_dump( $backtrace );
echo '<b>Fatal Error</b>: '.$errstr.' of class <b>'.$detail["class"].'</b> in <b>'.$detail["file"].'</b> on line <b>'.$detail["line"].'</b><br/>';
die();
}
private function fatal( $text ) {
set_error_handler( array( 'inheritance', 'error_die' ) );
trigger_error( $text, E_USER_ERROR );
restore_error_handler();
}
function __call( $name, $args ) {
if( $this->bases )
foreach( $this->bases as $base )
if( method_exists( $base, $name ) )
return $base->$name( $args );
$this->fatal( "Call to undefined method <b>".$name."</b>" );
}
function __set( $name, $value ) {
if( $this->bases )
foreach( $this->bases as $base )
if( property_exists( $base, $name ) ) {
$base->$name = $value;
return;
}
}
function __get( $name ) {
if( $this->bases )
foreach( $this->bases as $base )
if( property_exists( $base, $name ) )
return $base->$name;
}
function __isset( $name ) {
if( $this->bases )
foreach( $this->bases as $base )
if( property_exists( $base, $name ) )
return isset( $base->$name );
}
function __unset( $name ) {
if( $this->bases )
foreach( $this->bases as $base )
if( property_exists( $base, $name ) ) {
unset( $base->$name );
return;
}
}
function inherits( $name, $args = '' ) {
return array_unshift( $this->bases, new $name( $args ) );
}
}
?>
Most of the qualities of multiple inheritance provided by this class are revealed by the following code:
<?php //test inheritance
class base0 {
public $base0var;
public $basevar;
function base0declare() {
echo 'I am base 0';
}
function basedeclare() {
self::base0declare() {
}
}
class base1 extends base0 { // simple linear inheritance here
public $base1var;
public $basevar;
function based1declare() {
echo 'I am base 1';
}
function basedeclare() {
self::base1declare()
}
}
class base2
public $base2var;
public $basevar;
function based2declare() {
echo 'I am base 2';
}
function basedeclare() {
self::base2declare
}
}
?>
Multiple inheritance is achieved by extending the inheritance class, and then in the __construct function placing calls to the "inherits" method of the inheritance class. Each call pushes an instance of the inherited class into an array var which functions as a LIFO stack. Using the magic methods, any failed method call, property set, get, isset or unset is intercepted by the inheritance base class which then attempts to resolve the reference. Object method name conflicts are resolved simply by the later inheritance masking the scope of the earlier inherited method. I recognize there are shortcomings to the approach I offer here, but it works for all my current multiple inheritance needs and offers simplicity and ease of understanding as benefits.
<?php
class base_test extends inheritance { // multiple inheritance
function __construct() {
$this->inherits( 'base1' );
$this->inherits( 'base2' );
}
} ?>
Here are some code fragments you can try out to test things.
<?php
$testobj = new base_test();
var_dump( $testobj );
$testobj->base2declare();
$testobj->base1declare();
$testobj->base0declare();
$testobj->basedeclare();
$testobj->base2var = 27;
echo $testobj->base2var;
?>
I'd be interested in hearing any comments.
chris (@) xeneco (dot) co (dot) uk
27-Nov-2008 03:25
Regarding object inheritance:
I hope this helps someone, it should help if you're new to OOPS
<?php
class A {
public $x = 'A';
public function foo() {
$b = new B;
$b->bar();
return $this->x;
}
}
class B extends A {
public function bar() {
$this->x = 'B';
}
}
$a = new A
echo $a->foo(); //A
?>
I was doing something similar to this (example is greatly simplified to show logic) and spent a long while trying to work out why I would always get 'A' and never get 'B'. Now, after a few weeks, I have revisited the problem and have worked out why:
The code 'new B' creates a new instance of class B. While class B extends class A, it is a new object and not an extension of the object created by 'new A'
The value of $x is set to 'B' within the object $b, but not in object $a.
If within A::foo(), one was to access $b->x then one would obtain the vale 'B', for example
<?php
class C {
public $x = 'C';
public function foo() {
$c = new C;
$c->bar();
$this->x = $c->$x
return $this->x;
}
}
class D extends C {
public function bar() {
$this->x = 'D';
}
}
$c = new C
echo $c->foo(); //D
?>
Jeffrey
08-Oct-2008 03:49
A PHP Class can be used for several things, but at the most basic level, you'll use classes to "organize and deal with like-minded data". Here's what I mean by "organizing like-minded data". First, start with unorganized data.
<?php
$customer_name;
$item_name;
$item_price;
$customer_address;
$item_qty;
$item_total;
?>
Now to organize the data into PHP classes:
<?php
class Customer {
$name; // same as $customer_name
$address; // same as $customer_address
}
class Item {
$name; // same as $item_name
$price; // same as $item_price
$qty; // same as $item_qty
$total; // same as $item_total
}
?>
Now here's what I mean by "dealing" with the data. Note: The data is already organized, so that in itself makes writing new functions extremely easy.
<?php
class Customer {
public $name, $address; // the data for this class...
// function to deal with user-input / validation
// function to build string for output
// function to write -> database
// function to read <- database
// etc, etc
}
class Item {
public $name, $price, $qty, $total; // the data for this class...
// function to calculate total
// function to format numbers
// function to deal with user-input / validation
// function to build string for output
// function to write -> database
// function to read <- database
// etc, etc
}
?>
Imagination that each function you write only calls the bits of data in that class. Some functions may access all the data, while other functions may only access one piece of data. If each function revolves around the data inside, then you have created a good class.
wbcarts at juno dot com
20-Aug-2008 06:11
CLASSES and OBJECTS that represent the "Ideal World"
Wouldn't it be great to get the lawn mowed by saying $son->mowLawn()? Assuming the function mowLawn() is defined, and you have a son that doesn't throw errors, the lawn will be mowed.
In the following example; let objects of type Line3D measure their own length in 3-dimensional space. Why should I or PHP have to provide another method from outside this class to calculate length, when the class itself holds all the neccessary data and has the education to make the calculation for itself?
<?php
/*
* Point3D.php
*
* Represents one locaton or position in 3-dimensional space
* using an (x, y, z) coordinate system.
*/
class Point3D
{
public $x;
public $y;
public $z; // the x coordinate of this Point.
/*
* use the x and y variables inherited from Point.php.
*/
public function __construct($xCoord=0, $yCoord=0, $zCoord=0)
{
$this->x = $xCoord;
$this->y = $yCoord;
$this->z = $zCoord;
}
/*
* the (String) representation of this Point as "Point3D(x, y, z)".
*/
public function __toString()
{
return 'Point3D(x=' . $this->x . ', y=' . $this->y . ', z=' . $this->z . ')';
}
}
/*
* Line3D.php
*
* Represents one Line in 3-dimensional space using two Point3D objects.
*/
class Line3D
{
$start;
$end;
public function __construct($xCoord1=0, $yCoord1=0, $zCoord1=0, $xCoord2=1, $yCoord2=1, $zCoord2=1)
{
$this->start = new Point3D($xCoord1, $yCoord1, $zCoord1);
$this->end = new Point3D($xCoord2, $yCoord2, $zCoord2);
}
/*
* calculate the length of this Line in 3-dimensional space.
*/
public function getLength()
{
return sqrt(
pow($this->start->x - $this->end->x, 2) +
pow($this->start->y - $this->end->y, 2) +
pow($this->start->z - $this->end->z, 2)
);
}
/*
* The (String) representation of this Line as "Line3D[start, end, length]".
*/
public function __toString()
{
return 'Line3D[start=' . $this->start .
', end=' . $this->end .
', length=' . $this->getLength() . ']';
}
}
/*
* create and display objects of type Line3D.
*/
echo '<p>' . (new Line3D()) . "</p>\n";
echo '<p>' . (new Line3D(0, 0, 0, 100, 100, 0)) . "</p>\n";
echo '<p>' . (new Line3D(0, 0, 0, 100, 100, 100)) . "</p>\n";
?>
<-- The results look like this -->
Line3D[start=Point3D(x=0, y=0, z=0), end=Point3D(x=1, y=1, z=1), length=1.73205080757]
Line3D[start=Point3D(x=0, y=0, z=0), end=Point3D(x=100, y=100, z=0), length=141.421356237]
Line3D[start=Point3D(x=0, y=0, z=0), end=Point3D(x=100, y=100, z=100), length=173.205080757]
My absolute favorite thing about OOP is that "good" objects keep themselves in check. I mean really, it's the exact same thing in reality... like, if you hire a plumber to fix your kitchen sink, wouldn't you expect him to figure out the best plan of attack? Wouldn't he dislike the fact that you want to control the whole job? Wouldn't you expect him to not give you additional problems? And for god's sake, it is too much to ask that he cleans up before he leaves?
I say, design your classes well, so they can do their jobs uninterrupted... who like bad news? And, if your classes and objects are well defined, educated, and have all the necessary data to work on (like the examples above do), you won't have to micro-manage the whole program from outside of the class. In other words... create an object, and LET IT RIP!
ashraf dot samhouri at hotmail dot com
24-May-2008 06:35
@info -- 20-April
This is because you requested class "b" before defining it, not because you defined class "b" before "a". It doesn't make a difference which class you define first.
info at youwanttoremovethisvakantiebaas dot nl
20-Apr-2008 03:40
if you do this
<?php
$x = new b();
class b extends a {}
class a { }
?>
PHP will tell you "class b not found", because you've defined class b before a. However, the error tells you something different.... Got me a little confused :)
david dot schueler at tel-billig dot de
15-Feb-2008 06:16
If you just want to create a new object that extends another object and you want to copy all variables from the father object, you may use this piece of code:
<?php
$father =& new father();
$father->a_var = "Hello World.";
$son = new son($event);
$son->say_hello();
class father {
public $a_var;
}
class son extends father {
public function __construct($father_class) {
foreach ($father_class as $variable=>$value) {
$this->$variable = $value;
}
}
public function say_hello() {
echo "Son says: ".$this->a_var;
}
}
?>
This outputs:
Son says: Hello World.
So you dont have to clone the entire object to get the contents of the variables from the father object.
aaron at thatone dot com
15-Dec-2007 06:46
I was confused at first about object assignment, because it's not quite the same as normal assignment or assignment by reference. But I think I've figured out what's going on.
First, think of variables in PHP as data slots. Each one is a name that points to a data slot that can hold a value that is one of the basic data types: a number, a string, a boolean, etc. When you create a reference, you are making a second name that points at the same data slot. When you assign one variable to another, you are copying the contents of one data slot to another data slot.
Now, the trick is that object instances are not like the basic data types. They cannot be held in the data slots directly. Instead, an object's "handle" goes in the data slot. This is an identifier that points at one particular instance of an obect. So, the object handle, although not directly visible to the programmer, is one of the basic datatypes.
What makes this tricky is that when you take a variable which holds an object handle, and you assign it to another variable, that other variable gets a copy of the same object handle. This means that both variables can change the state of the same object instance. But they are not references, so if one of the variables is assigned a new value, it does not affect the other variable.
<?php
// Assignment of an object
Class Object{
public $foo="bar";
};
$objectVar = new Object();
$reference =& $objectVar;
$assignment = $objectVar
//
// $objectVar --->+---------+
// |(handle1)----+
// $reference --->+---------+ |
// |
// +---------+ |
// $assignment -->|(handle1)----+
// +---------+ |
// |
// v
// Object(1):foo="bar"
//
?>
$assignment has a different data slot from $objectVar, but its data slot holds a handle to the same object. This makes it behave in some ways like a reference. If you use the variable $objectVar to change the state of the Object instance, those changes also show up under $assignment, because it is pointing at that same Object instance.
<?php
$objectVar->foo = "qux";
print_r( $objectVar );
print_r( $reference );
print_r( $assignment );
//
// $objectVar --->+---------+
// |(handle1)----+
// $reference --->+---------+ |
// |
// +---------+ |
// $assignment -->|(handle1)----+
// +---------+ |
// |
// v
// Object(1):foo="qux"
//
?>
But it is not exactly the same as a reference. If you null out $objectVar, you replace the handle in its data slot with NULL. This means that $reference, which points at the same data slot, will also be NULL. But $assignment, which is a different data slot, will still hold its copy of the handle to the Object instance, so it will not be NULL.
<?php
$objectVar = null;
print_r($objectVar);
print_r($reference);
print_r($assignment);
//
// $objectVar --->+---------+
// | NULL |
// $reference --->+---------+
//
// +---------+
// $assignment -->|(handle1)----+
// +---------+ |
// |
// v
// Object(1):foo="qux"
?>
alan at alan-ng dot net
09-Oct-2007 09:41
The following odd behavior happens in php version 5.1.4 (and presumably some other versions) that does not happen in php version 5.2.1 (and possibly other versions > 5.1.4).
<?php
$_SESSION['instance']=...;
$instance=new SomeClass;
?>
The second line will not only create the $instance object successfully, it will also modify the value of $_SESSION['instance']!
The workaround I arrived at, after trial and error, was to avoid using object names which match a $_SESSION array key.
This is not intended to be a bug report, since it was apparently fixed by version 5.2.1, so it's just a workaround suggestion.
Dan Dascalescu
26-Oct-2006 11:00
If E_STRICT is enabled, the first example will generate the following error (and a few others akin to it):
Non-static method A::foo() should not be called statically on line 26
The example should have explicitly declared the methods foo() and bar() as static:
class A
{
static function foo()
{
...