클래스와 객체
Tilman I think you are little bit confused about get_parent_class() function.
Actually this function return the 'parent class' of the class, object belong to; with which it is called.
In your example one_get_parent_class_name() and two_get_parent_class_name() are similar functions and are located in different classes. Their behaviour will be same if will be called with same object. Just add the following two line at the end. You will get the better understanding.
$two=new two();
$two->two_get_parent_class_name();
extends
때때로 기존의 클래스와 비슷한 변수와 함수를 갖는 클래스가 필요할때 가 있다. 실제로, 모든 프로젝트에서 사용할수 있는 범용의 클래스를 선언하고, 특정 프로젝트에서 이런 클래스를 필요에 의해 변경하는 것은 좋은 습관이다. 이런 일을 수월하게 하기 위해서 클래스는 다른 클래스에서 확장(extension) 될수 있다. 이렇게 확장되거나 파생된 클래스는 원래 클래스의 모든 변수와 함수를 소유하고 (이런 경우를 아무도 죽지 않았음 에도 불구하고 '상속'이라고 부른다) 필요로 하는 확장된 선언을 추가할수 있다. 기존 클래스에서 기존 함수나 변수의 선언을 해제하여 뺄수는 없다. 확장 클래스는 항상 하나의 기존 클래스에만 연관되어있다. 즉 다중 상속은 지원되지 않는다. 클래스는 'extends'라는 키워드를 사용하여 확장된다.
<?php
class Named_Cart extends Cart
{
var $owner;
function set_owner ($name)
{
$this->owner = $name;
}
}
?>
위 코드는 Cart의 모든 변수와 함수는 물론 추가된 변수 $owner 와 추가된 함수 set_owner()를 갖는 클래스를 선언한다. 이로써 이름이 있는 카트를 만들고 카트의 소유자를 설정하고 얻어올수 있다. 이름이 있는 카트에서는 물론 기존의 일반 카트 함수 도 쓸수 있다:
<?php
$ncart = new Named_Cart; // 이름이 있는 카트 만들기
$ncart->set_owner("kris"); // 그 카트에 소유자를 설정
print $ncart->owner; // 소유자 이름을 출력
$ncart->add_item("10", 1); // (기존 cart에서 상속한 함수 사용)
?>
이런 경우를 "부모-자식" 관계라고 부르기도 한다. 부모 클래스를 만들고, 부모 클래스에 기반한 새 클래스를 만들려면 extends를 사용한다: 자식 클래스. 심지어 이런 새로운 자식 클래스를 사용하거나 이 자식 클래스에 기반한 다른 클래스도 만들수 있다.
Note: 클래스는 그것이 사용되기 전에 이미 선언되어 있어야 한다! Cart클래스를 상속하는 Named_Cart클래스가 필요하면 우선 Cart클래스를 먼저 선언해야 할것이다. Named_Cart클래스에 기반한 다른 클래스 Yellow_named_cart 를 생성하고자 한다면 Named_Cart클래스를 먼저 선언해야 한다. 짧게 말해서: 클래스가 선언되는 순서는 중요하다.
add a note
User Contributed Notesextends
Neelam Bhatt
10-May-2006 02:44
10-May-2006 02:44
Edward_nl
03-Mar-2006 02:54
03-Mar-2006 02:54
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 $p->My_test();
// Returns 3
doedje
12-Feb-2006 01:37
12-Feb-2006 01:37
tilman's note is not quite true. He states the fact that php gives wrong information about the parent class. But this is not the case. Php does give correct information about the parent class, to prove that I give the following code:
<?php
class a
{
function showInfo()
{
print "I am class " . get_class($this) . ", my parent is " .get_parent_class($this);
}
}
class b extends a {}
class c extends b {}
$myInstanceB = new b();
$myInstanceB->showInfo();
print "<br />";
$myInstanceC = new c();
$myInstanceC->showInfo();
/*
output:
I am class b, my parent is a
I am class c, my parent is b
*/
?>
The thing is the function showInfo as they were called by my script, are not a member of class a, but are a member of class b and c. They respond accordingly. Showing correct output in the case of get_class and get_parent_class. So don't go blaming php! =]
tilman dot schroeder at gmx dot de
19-Jan-2006 11:24
19-Jan-2006 11:24
Hi...
as alan hogan pointed out it is possible to inherit a class from multiple other classes but notice that php does not always give you the right name of the parent class if you are deriving from multiple classes (tested on php 4.4.0):
<?php
header("Content-Type: text/plain");
class three {
function three() {
echo("constructor of three\n");
} // end function three
} // end class three
class two extends three {
function two() {
echo("constructor of two\n");
} // end function two
function two_get_parent_class_name() {
echo("i am two and my parent is: ".get_parent_class($this)."\n");
} // end one_function get_parent_class_name()
} // end class two
class one extends two {
function one() {
echo("constructor of one\n");
} // end function one
function one_get_parent_class_name() {
echo("i am one and my parent is: ".get_parent_class($this)."\n");
} // end one_function get_parent_class_name()
} // end class one
$one=new one();
$one->two();
$one->three();
$one->one_get_parent_class_name();
$one->two_get_parent_class_name();
/*
* will print out:
*
* constructor of one
* constructor of two
* constructor of three
* i am one and my parent is: two
* i am two and my parent is: two // should print out "my parent is: three"
*/
?>
So be careful when dealing with parents within classes ...
However, if you are using parent:: it will give you access to BOTH parent classes:
<?php
header("Content-Type: text/plain");
class three {
function three() {
echo("three\n");
}
}
class two extends three {
function two() {
echo("two\n");
}
}
class one extends two {
function one() {
echo("one\n");
parent::two();
parent::three();
}
}
one::one();
/*
* will print out:
* one
* two
* three
*/
?>
alan hogan
26-Nov-2005 05:48
26-Nov-2005 05:48
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.
18-Nov-2005 09:43
18-Nov-2005 09:43
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);
}
?>
mga at nrd dot lt
18-Apr-2005 07:03
18-Apr-2005 07:03
[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
The example listed above does not show the main advantages of multiple inheritance. I mean, that multiple inheritance is used not for different outputs, but to combain properties ant functionality from different classes.
If you will try to create complex structure based on this example, I am sure, will be big problems regarding member variables values and etc.
In example, each time when you use "inherited" class it is temporarily created!
The main advantage of inheritance is direct incapsulation of member variables and functions. And here are no possibility to use this advantage :(
volte6 at nowhere dot com
31-Mar-2005 10:11
31-Mar-2005 10:11
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
06-Mar-2005 05:19
06-Mar-2005 05:19
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.
Roy Yong
27-Jan-2005 08:37
27-Jan-2005 08:37
I'm not sure if i'm outdated but I think the current PHP version still does not support extension of methods (something that stands between polymorphism and overriding). Hopefully, this could be included in the next release version of PHP!
jo at durchholz dot org
17-Dec-2004 08:54
17-Dec-2004 08:54
Multiple inheritance, if designed properly into the language, most definitely is worth the trouble. Solutions exist for all associated problems (including the name clash issue mentioned above - identify a function by adding the name of the class where is was first defined, and all ambiguities vanish; make the class identification optional if nonambiguous, and it's even backwards-compatible).
The rub is that it's difficult to get a language design that's simple to use, efficiently implementable, and applicable to a dynamically-typed language like PHP.
Msquared
19-Nov-2004 06:48
19-Nov-2004 06:48
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
]]
Dave Fancella
14-Mar-2004 07:09
14-Mar-2004 07:09
I recommend against using the examples here given for multiple inheritance.
The essential problem is having readable code. If you want to be able to read your code in a few months, or if you want others to be able to read your code, you're better off using member variables to store class instances than using hacked on multiple inheritance.
One of the big advantages to multiple inheritance in a language that properly supports it like C++ is that you can see, in the class declaration, what it inherits from. In the example where you extend some class called MultipleInheritance, that only obfuscates your class's ancestry.
So, use inheritance, it's good. But it's not the be all end all of solutions. If it were, we wouldn't have templates and various other things in C++. So don't depend on it. Instead of asking yourself "How do I use inheritance to solve this problem?" you should ask yourself "Is inheritance the right tool to solve this problem?" If the language doesn't support multiple inheritance and you're trying to use it anyway, then you have certainly chosen the wrong tool to solve your problem.
efredin at redtempest dot com
02-Mar-2004 05:35
02-Mar-2004 05:35
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).
<?
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();
?>
robertvanderlinden78 at hotmail dot com
18-Oct-2003 11:50
18-Oct-2003 11:50
the model as in the example of "quinton" is what you want to have. Not the method of "kimh216" with function callClass
when calling
function C()
{
//global $a,$b;
$this->a = parent::callClass('A');//no effect
$this->b = parent::callClass('B');//no effect
}
you will not have 1 data object.If i wanted to add a function to class A and i wanted to call it , I can only do it from Class C .. otherwise if I were to do
$c = new C();
$c->someExtraFunctionThatIsInClassA(); it will give an error stating "Fatal error: Call to undefined function: functionName() in f:\ibserver\www\meuk\classvbs\test.php.php on line 34"
------------
If i add a new function in Person class of the first example of quinton:
function boe(){
echo "some text";
}
then i can call it by :
$family->members[0]->boe();
since the members array has Personobjects in it. Now you have 1 Object that can access every function as a whole.
regards rml
mazsolt at yahoo dot com
04-Jul-2003 08:49
04-Jul-2003 08:49
Just a simple example about inheritance:
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
22-Jun-2003 08:58
22-Jun-2003 08:58
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 :
<?
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 01:07
10-Jun-2003 01:07
a nice example using extends and multiple classes and constructors.
<?
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);
?>
j237fl at hotmail dot com
26-Feb-2003 06:28
26-Feb-2003 06:28
This code fragment does NOT seem to work. It seems as though, the PHP engine when loading a class dosen't set the member vars FIRST, it seems as though it loads the BasicLife member vars before the Super Class methods.
class BasicLife extends Benefit{
//MEMBER VAR simply REFERS TO METHOD OF SUPER CLASS
var $simply = Benefit::get_simply();
//MEMBER VAR me REFERS TO METHOD OF THIS->CLASS
var $me = $this->get_me();
function BasicLife(){//CONSTRUCTOR}
function get_me(){}
}
kimh216 at hotmail dot com
28-Oct-2002 05:19
28-Oct-2002 05:19
I made some change...
If you don't want to call parent::callClass('A') on the every function which have to call it's parent's method.
//multipleInheritance
class multipleInheritance
{
function callClass($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
{
var $a;
var $b;
function C()
{
//global $a,$b;
$this->a = parent::callClass('A');//no effect
$this->b = parent::callClass('B');//no effect
}
function insideA()
{
// global $a,$b;
$this->a->insideA();
}
function insideB()
{
//global $a,$b;
$this->b->insideB();
}
function insideC()
{
echo("I'm inside C!<BR>");
}
}
$c = new C();
$c->insideA();
$c->insideB();
$c->insideC();
novaki at dcs dot vein dot hu
20-Oct-2002 10:13
20-Oct-2002 10:13
inheritance from multiple parent classes:
// won't work
class myChildClass extends pClass1, pClass2 {
}
PHP uses aggregation for inheriting from multiple parents, which I think is a bit more complex. See the aggregate function.
(my personal oppinion is that the first method of multiple inheritance should also be imlemented, but I got the answer that it won't be fixed)
"inerte" is my hotmail.com username
27-Sep-2002 01:36
27-Sep-2002 01:36
[Editor's note: For an alternative to multiple inheritance, see the dynamic binding via object aggregation in the corresponding section of the manual.]
Multiple Inheritance is not supported but it is easy to emulate it:
class multipleInheritance
{
function callClass($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
15-Aug-2002 10:37
15-Aug-2002 10:37
class a {
function samename(){
echo 'a';
} }
class b extends a{
function samename(){
echo 'b';
}
function b(){
a::samename();
b::samename();
} }
$test_obj = new b();
Quiet confusing though, as this prints out 'ab'.
No need to create a new instance of a,
therefor both methods still exists with same name.
griffon9 at hotmail dot com
18-Jul-2002 04:42
18-Jul-2002 04:42
Just to clarify something about inheritance. The following code :
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 11:31
11-Dec-2001 11:31
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:
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 12:08
07-Nov-2001 12:08
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 {
...
}
...
?>