class
If you are using a child-class. Remember to call the constructor of the parent class aswell before you start using it. Otherwise you might get different results then you expected. It is stated in this document, but I got confused by the given example. So, here is my example:
<?php
error_reporting(E_ALL);
class test {
var $var;
function test() {
$this->var = 3;
}
}
class testing extends test {
function testing() {
parent::test();
}
function My_test() {
return $this->var;
}
}
$p = new testing();
echo $p->My_test();
// Returns 3
extends
Много често имаме нужда от класове с променливи и функции подобни на тези от друг съществуващ клас. Всъщност е добра практика да дефинираме общ клас, който да може да се използва във всичките проекти и да адаптираме този клас за специфичните нужди на конкретния проект. За да се улесни това, класовете могат да наследяват други класове. Производният клас има всички променливи и функции на базовия клас (това се нарича 'наследство', въпреки факта, че никой не е умрял), както и тези които са допълнително дефинирани. Не е възможно да изваждате променливи или функции от производен клас, т.е. да премахвате вече дефинирани функции и променливи. Производният клас винаги наследява от един базов клас, т.е. множествено наследяване не се поддържа. Наследяването на класове се осъществява с ключовата дума 'extends' (разширява).
<?php
class Named_Cart extends Cart {
var $owner;
function set_owner ($name) {
$this->owner = $name;
}
}
?>
В горния пример е дефиниран клас Named_Cart, който притежава всички променливи и функции от Cart, плюс допълнителната променлива $owner и допълнителната функция set_owner(). Може да създадете именувана пазарска количка по нормалния начин и да установите или да върнете като резултат името на собственика й. Можете да използвате и функциите на нормалната пазарска количка върху именуваната такава:
<?php
$ncart = new Named_Cart; // Създаване на именувана пазарска количка
$ncart->set_owner("kris"); // Задаване на име на пазарската количка
print $ncart->owner; // извежда името на собственика на пазарската количка
$ncart->add_item("10", 1); // (наследена функционалност от Cart)
?>
Това също така се нарича отношение родител-наследник. Създавате родителски клас и използвате extends, за да създадете нов клас базиран на родителския: дъщерен клас. Можете да използвате този дъщерен клас, за да дефинират друг клас базиран на него.
Забележка: Класовете трябва да бъдат дефинирани преди да бъдат използвани! Ако искате клас Named_Cart да наследи клас Cart, трябва първо да дефинирате клас Cart. Ако искате да създадете друг клас наречен Yellow_named_cart, наследяващ класа Named_Cart, ще трябва първо да дефинирате Named_Cart. Накратко: редът на дефиниране на класовете е важен.
add a note
User Contributed Notesextends
Edward_nl
03-Mar-2006 10:54
03-Mar-2006 10:54
alan hogan
27-Nov-2005 01:48
27-Nov-2005 01:48
Just a note: It is possible to have a class inherit from multiple other classes, but only in a one-at-a-time linear hierarchy.
So this works, and C gets A and B functions:
<?php
class A {
public function af() { print 'a';}
public function bark() {print ' arf!';}
}
class B extends A {
public function bf() { print 'b';}
}
class C extends B {
public function cf() { print 'c';}
public function bark() {print ' ahem...'; parent::bark();}
}
$c = new C;
$c->af(); $c->bf(); $c->cf();
print "<br />";
$c->bark();
/**results:**/
//abc
//ahem... arf!
?>
This does NOT work:
<?php
class A {
public function af() { print 'a';}
public function bark() {print ' arf!';}
}
class B {
public function bf() { print 'b';}
}
class C extends B, A /*illegal*/ {
public function cf() { print 'c';}
public function bark() {print ' ahem...'; parent::bark();}
}
$c = new C;
$c->af(); $c->bf(); $c->cf();
print "<br />";
$c->bark();
//Parse Error
?>
Bash I.
19-Nov-2005 05:43
19-Nov-2005 05:43
Here is a simple idea that I use when I need my abstract classes (the inherited classes) implemented before my functional classes.
<?php
$_CLASSES = array_merge (
glob ("classes/*/*.abstract.php"),
glob ("classes/*/*.class.php")
);
foreach ($_CLASSES AS $_CLASS) {
require ($_CLASS);
}
?>
volte6 at nowhere dot com
31-Mar-2005 06:11
31-Mar-2005 06:11
When declaring a class that relies upon another file ( because it extends the class defined in that file ), you should ALWAYS require_once() that file at the top.
This applies even when planning on looping through and including everything in the folder. Use require_once() in your loop, and at the top of the file that NEEDS the include.
tomnezvigin at comcast dot net
07-Mar-2005 01:19
07-Mar-2005 01:19
This may seem obvious, but check this scenario. You have a class folder:
+ class
--classA.php
--classB.php
--classC.php
--mainClass.php
Here... classA, classB, classC all extend the mainClass.
If you try to create a function that automatically includes all of the classes in a folder, normally, they are included alphabetically.
When you try to instantiate classC, for example, you will get an error:
"Cannot inherit from undefined class mainClass"
EVEN IF you instantiate the mainClass before you instantiate all of the other classes.
In other words, make sure your primary class is included before all others.
Msquared
19-Nov-2004 02:48
19-Nov-2004 02:48
Multiple inheritence is often more trouble than it's worth. For example, you have a class foo that inherits from both class bar and class baz. Classes bar and baz both have a fubar() method. When you create a foo object and call its fubar() method, which fubar() method is called: bar's or baz's?
It seems to me that using aggregate to glue one class's methods and data to another object is a bit like Ruby's fixins, but I could be wrong...
[[Editor's note:
The aggregate_* functions have been dropped, as of PHP 5
-S
]]
efredin at redtempest dot com
03-Mar-2004 01:35
03-Mar-2004 01:35
It is possible to override a method innherited from a parent class by simply re-defining the method (for those of us who enjoy using abstract classes).
<?php
class A
{
var $foo;
function A()
{
$this->foo = "asdf";
}
function bar()
{
echo $this->foo." : Running in A";
}
}
class B extends A
{
function bar()
{
echo $this->foo." : Running in B";
}
}
$myClass = new B;
$myClass->bar();
?>
mazsolt at yahoo dot com
04-Jul-2003 03:49
04-Jul-2003 03:49
Just a simple example about inheritance:
<?php
class a1{
var $a=10;
function a1($a){
$this->a=$a;
}
}
class a2 extends a1{
var $x=11;
function a2($x,$y){
$this->x=$x;
parent::a1($y); // or a1::a1($y) or $this->a1($y)
}
}
class a3 extends a2{
var $q=999;
}
$x=new a3(99,9);
echo $x->a,"<br>",$x->x,"<br> ",$x->q;
?>
The output will be:
9
99
999
calimero at creatixnet dot com
23-Jun-2003 03:58
23-Jun-2003 03:58
Just a quick note to make things more clear : while multiple inheritance is not allowed, several levels of single inheritance ARE ALLOWED indeed. Just test this example :
<?php
class A {
var $name='A';
function disp() {
echo $this->name;
}
}
class B extends A {
var $name='B';
}
class C extends B {
var $name='C';
}
$truc = new C() ;
$truc->disp(); // Will output C
?>
This is especially important to keep in mind while building a huge object hierarchy. for example :
+GenericObject
->+ Person
->->Employee
->+Computer
->->+WorkStation
->->-> PPC
->->-> Intel
->->+Server
->->->LDAPServer
->->->IntranetWebServer
.. and so on. Multiple level hierarchy relationship are possible in a tree-like structure (each child has one and only one parent, except for the root object).
quinton at free dot fr
10-Jun-2003 08:07
10-Jun-2003 08:07
a nice example using extends and multiple classes and constructors.
<?php
class CoreObject {
var $name;
function CoreObject($name){
$this->_constructor($name);
}
function _constructor($name){
$this->name = $name;
}
function show(){
printf("%s::%s\n", $this->get_class(), $this->name);
}
function get_class(){
return get_class($this);
}
}
class Container extends CoreObject{
var $members;
function Container($name){
$this->_constructor($name);
}
function &add(&$ref){
$this->members[] = $ref;
return ($ref);
}
function show(){
parent::show();
foreach($this->members as $item){
$item->show();
}
}
function apply(){
}
}
class Person extends CoreObject{
function Person($name){
$this->_constructor($name);
}
}
class Family extends Container {
var $members;
function Family($name){
$this->_constructor($name);
}
}
echo "<pre>\n";
$family = new Family('my family');
$family->add(new Person('father'));
$family->add(new Person('mother'));
$family->add(new Person('girl'));
$family->add(new Person('boy'));
$family->show();
print_r($family);
?>
"inerte" is my hotmail.com username
27-Sep-2002 08:36
27-Sep-2002 08:36
[Editor's note: For an alternative to multiple inheritance, see the dynamic binding via object aggregation in the corresponding section of the manual.]
Multiple Inheritance is not supported but it is easy to emulate it:
<?php
class multipleInheritance
{
function callClass($class_to_call)
{
return new $class_to_call();
}
}
class A
{
function insideA()
{
echo "I'm inside A!<br />";
}
}
class B
{
function insideB()
{
echo "I'm inside B!<br />";
}
}
class C extends multipleInheritance
{
function insideC()
{
$a = parent::callClass('A');
$a->insideA();
$b = parent::callClass('B');
$b->insideB();
}
}
$c = new C();
$c->insideC();
?>
---
This will succesfully echo:
I'm inside A!
I'm inside B!
schultz at rancon dot de
16-Aug-2002 05:37
16-Aug-2002 05:37
This prints out 'ab'. No need to create a new instance of a, therefor both methods still exists with same name.
<?php
class a {
function samename(){
echo 'a';
}
}
class b extends a{
function samename(){
echo 'b';
}
function b(){
a::samename();
b::samename();
}
}
$test_obj = new b();
?>
griffon9 at hotmail dot com
18-Jul-2002 11:42
18-Jul-2002 11:42
Just to clarify something about inheritance. The following code :
<?php
class a
{
function call()
{
$this->toto();
}
function toto()
{
echo('Toto of A');
}
}
class b extends a
{
function toto()
{
echo('Toto of B');
}
}
$b=new b;
$b->call();
?>
...will correctly display "toto of B" (that is, the function declared in the parent is correctly calling the redefined function in the child)
php_AT_undeen_DOT_com
11-Dec-2001 07:31
11-Dec-2001 07:31
if the class B that extends class A does not have a constuctor function (i.e. a function named B), then the constructor function of A will be used instead, you don't need to make a constructor in B just to call the constructor of A.
For example:
<?php
class A
{
function A()
{
echo "HEY! I'm A!\n";
}
}
class B extends A
{
}
$b = new B();
?>
produces the output:
HEY! I'm A!
bpotier at edreamers dot org
07-Nov-2001 08:08
07-Nov-2001 08:08
Just one thing that may seem obvious but not mentionned in this page is that you need to include/require the file containing the parent class or else you'll get an error:
<?php
require(dirname(__FILE__).'/'.'myParent.php');
// ...
myChild extends myParent {
// ...
}
// ...
?>