Интерфейсы объектов
Интерфейсы объектов позволяют создавать код, который указывает, какие методы и свойства должен включать класс, без необходимости описывания их функционала.
Интерфейсы объявляются так же, как и обычные классы, но с использованием ключевого слова interface. Тела методов интерфейсов должны быть пустыми.
Все методы, определенные в интерфейсы должны быть публичными, что следует из самой природы интерфейса.
implements
Для реализации интерфейса используется оператор implements. Класс должен реализовать все методы, описанные в интерфейсе; иначе произойдет фатальная ошибка. При желании классы могут реализовывать более одного интерфейса за раз, реализуемые интерфейсы должны разделяться запятой.
Замечание:
Класс не может реализовать два интерфейса, содержащих одноименную функцию, так как это повлечет за собой неоднозначность.
Замечание:
Интерфейсы могут быть унаследованы друг от друга, так же как и классы, с помощью оператора extends.
Замечание:
Сигнатуры методов в классе, реализующем интерфейс, должны точно совпадать с сигнатурами, используемыми в интерфейсе, в противном случае будет вызвана фатальная ошибка.
Константы (Constants)
Интерфейсы могут содержать константы. Константы интерфейсов работают точно так же, как и константы классов, за исключением того, что они не могут быть перекрыты наследующим классом или интерфейсом.
Примеры
Пример #1 Пример интерфейса
<?php
// Объявим интерфейс 'iTemplate'
interface iTemplate
{
public function setVariable($name, $var);
public function getHtml($template);
}
// Реализуем интерфейс
// Это сработает нормально
class Template implements iTemplate
{
private $vars = array();
public function setVariable($name, $var)
{
$this->vars[$name] = $var;
}
public function getHtml($template)
{
foreach($this->vars as $name => $value) {
$template = str_replace('{' . $name . '}', $value, $template);
}
return $template;
}
}
// Это не будет работать
// Fatal error: Class BadTemplate contains 1 abstract methods
// and must therefore be declared abstract (iTemplate::getHtml)
// (Фатальная ошибка: Класс BadTemplate содержит 1 абстрактный метод
// и поэтому должнен быть объявлен абстрактным (iTemplate::getHtml))
class BadTemplate implements iTemplate
{
private $vars = array();
public function setVariable($name, $var)
{
$this->vars[$name] = $var;
}
}
?>
Пример #2 Расширяемые интерфейсы
<?php
interface a
{
public function foo();
}
interface b extends a
{
public function baz(Baz $baz);
}
// Это сработает
class c implements b
{
public function foo()
{
}
public function baz(Baz $baz)
{
}
}
// Это не сработает и выдаст фатальную ошибку
class d implements b
{
public function foo()
{
}
public function baz(Foo $foo)
{
}
}
?>
Пример #3 Множественное наследование интерфейсов
<?php
interface a
{
public function foo();
}
interface b
{
public function bar();
}
interface c extends a, b
{
public function baz();
}
class d implements c
{
public function foo()
{
}
public function bar()
{
}
public function baz()
{
}
}
?>
Пример #4 Интерфейсы с константами
<?php
interface a
{
const b = 'Константа интерфейса';
}
// Выведет: Константа интерфейса
echo a::b;
// Вот это, однако, не будет работать, так как
// константы перекрывать нельзя.
class b implements a
{
const b = 'Class constant';
}
?>
Интерфейс, совместно с контролем типов, предоставляет отличный способ проверки того, что определенный объект содержит определенный набор методов. Смотрите также оператор instanceof и контроль типов.
- Введение
- Основы
- Свойства
- Константы классов
- Автоматическая загрузка классов
- Конструкторы и деструкторы
- Область видимости
- Наследование
- Оператор разрешения области видимости (::)
- Ключевое слово "static"
- Абстрактные классы
- Интерфейсы объектов
- Трейты
- Anonymous classes
- Перегрузка
- Итераторы объектов
- Магические методы
- Ключевое слово "final"
- Клонирование объектов
- Сравнение объектов
- Контроль типа
- Позднее статическое связывание
- Объекты и ссылки
- Сериализация объектов
- Журнал изменений ООП
Коментарии
You can also specify class constants in interfaces as well (similar to specifying 'public static final' fields in Java interfaces):
<?php
interface FooBar
{
const SOME_CONSTANT = 'I am an interface constant';
public function doStuff();
}
?>
Then you can access the constant by referring to the interface name, or an implementing class, (again similar to Java) e.g.:
<?php
class Baz implements FooBar
{
//....
}
print Baz::SOME_CONSTANT;
print FooBar::SOME_CONSTANT;
?>
Both of the last print statements will output the same thing: the value of FooBar::SOME_CONSTANT
interfaces support multiple inheritance
<?php
interface SQL_Result extends SeekableIterator, Countable
{
// new stuff
}
abstract class SQL_Result_Common
{
// just because that's what one would do in reality, generic implementation
}
class SQL_Result_mysql extends SQL_Result_Common implements SQL_Result
{
// actual implementation
}
?>
This code raises a fatal error because SQL_Result_mysql doesn't implement the abstract methods of SeekableIterator (6) + Countable (1)
When should you use interfaces? What are they good for?
Here are two examples.
1. Interfaces are an excellent way to implement reusability.
You can create a general interface for a number of situations
(such as a save to/load from disk interface.) You can then
implement the interface in a variety of different ways (e.g. for
formats such as tab delimited ASCII, XML and a database.)
You can write code that asks the object to "save itself to
disk" without having to worry what that means for the object
in question. One object might save itself to the database,
another to an XML and you can change this behavior over
time without having to rewrite the calling code.
This allows you to write reusable calling code that can work
for any number of different objects -- you don't need to know
what kind of object it is, as long as it obeys the common
interface.
2. Interfaces can also promote gradual evolution. On a
recent project I had some very complicated work to do and I
didn't know how to implement it. I could think of a "basic"
implementation but I knew I would have to change it later.
So I created interfaces in each of these cases, and created
at least one "basic" implementation of the interface that
was "good enough for now" even though I knew it would have
to change later.
When I came back to make the changes, I was able to create
some new implementations of these interfaces that added the
extra features I needed. Some of my classes still used
the "basic" implementations, but others needed the
specialized ones. I was able to add the new features to the
objects themselves without rewriting the calling code in most
cases. It was easy to evolve my code in this way because
the changes were mostly isolated -- they didn't spread all
over the place like you might expect.
The statement, that you have to implement _all_ methods of an interface has not to be taken that seriously, at least if you declare an abstract class and want to force the inheriting subclasses to implement the interface.
Just leave out all methods that should be implemented by the subclasses. But never write something like this:
<?php
interface Foo {
function bar();
}
abstract class FooBar implements Foo {
abstract function bar(); // just for making clear, that this
// method has to be implemented
}
?>
This will end up with the following error-message:
Fatal error: Can't inherit abstract function Foo::bar() (previously declared abstract in FooBar) in path/to/file on line anylinenumber
Classes and interface names share a common name space, so you can't have a class and an interface with the same name, even though the two can never be used ambiguously (i.e. there are no circumstances in which a class and an interface can be used interchangeably). e.g. this will not work:
interface foo {
public function bling();
}
class foo implements foo {
public function bling() {
}
}
You will get a 'Cannot redeclare class' error, even though it's only been declared as a class once.
on the post below:
An interface is in fact the same like an abstract class containing abstract methods, that's why interfaces share the same namespace as classes and why therefore "real" classes cannot have the same name as interfaces.
To two notes below: There is one situation where classes and interfaces can be used interchangeably. In function definitions you can define parameter types to be classes or interfaces. If this was not so then there would not be much use for interfaces at all.What is not mentioned in the manual is that you can use "self" to force object hinting on a method of the implementing class:
Consider the following interface:
<?php
interface Comparable
{function compare(self $compare);}
?>
Which is then implemented:
<?php
class String implements Comparable
{
private $string;
function __construct($string)
{$this->string = $string;}
function compare(self $compare)
{return $this->string == $compare->string;}
}
class Integer implements Comparable
{
private $integer;
function __construct($int)
{$this->integer = $int;}
function compare(self $compare)
{return $this->integer == $compare->integer;}
}
?>
Comparing Integer with String will result in a fatal error, as it is not an instance of the same class:
<?php
$first_int = new Integer(3);
$second_int = new Integer(3);
$first_string = new String("foo");
$second_string = new String("bar");
var_dump($first_int->compare($second_int)); // bool(true)
var_dump($first_string->compare($second_string)); // bool(false)
var_dump($first_string->compare($second_int)); // Fatal Error
?>
Note that you can extend interfaces with other interfaces since under-the-hood they are just abstract classes:
<?php
interface Foo {
public function doFoo();
}
interface Bar extends Foo {
public function doBar();
}
class Zip implements Bar {
public function doFoo() {
echo "Foo";
}
public function doBar() {
echo "Bar";
}
}
$zip = new Zip();
$zip->doFoo();
$zip->doBar();
?>
This is quite useful when you're using interfaces for identity more than the rigidity it places upon an API. You can get the same result by implementing multiple interfaces.
An example of where I've used this in the past is with EventListener objects ala Java's Swing UI. Some listeners are effectively the same thing but happen at different times therefore we can keep the same API but change the naming for clarity.
if you want to implement an interface and in addition to use inheritance, first it uses “extends” and then “implements” example:
<?php
class MyChildClass extends MyParentClass implements MyInterface
{
// definition
}
?>
Regarding my previous note (04-Jul-2007 9:01):
I noticed a minor but critical mistake in my explanation. After the link to the PHP manual page on class abstraction, I stated:
"So by definition, you may only overload non-abstract methods."
This is incorrect. This should read:
"So by definition, you may only override non-abstract methods."
Sorry for any confusion.
On an incidental note, it is not necessary for the implementation of an interface method to use the same variable names for its parameters that were used in the interface declaration.
More significantly, your interface method declarations can include default argument values. If you do, you must specify their implementations with default arguments, too. Just like the parameter names, the default argument values do not need to be the same. In fact, there doesn't seem to be any functionality to the one in the interface declaration at all beyond the fact that it is there.
<?php
interface isStuffed {
public function getStuff($something=17);
}
class oof implements isStuffed {
public function getStuff($a=42) {
return $a;
}
}
$oof = new oof;
echo $oof->getStuff();
?>
Implementations that try to declare the method as getStuff(), getStuff($a), or getStuff($a,$b) will all trigger a fatal error.
If it's not already obvious, it's worth noticing that the parameters in the interface's method declaration do not have to have the same names as those in any of its implementations.
More significantly, default argument values may be supplied for interface method parameters, and they have to be if you want to use default argument values in the implemented classes:
<?php
interface isStuffable
{
public function getStuffed($ratio=0.5);
}
class Turkey implements isStuffable
{
public function getStuffed($stuffing=1)
{
// ....
}
}
?>
Note that not only do the parameters have different names ($ratio and $stuffing), but their default values are free to be different as well. There doesn't seem to be any purpose to the interface's default argument value except as a dummy placeholder to show that there is a default (a class implementing isStuffable will not be able to implement methods with the signatures getStuffed(), getStuffed($a), or getStuffed($a,$b)).
In case you would want to, a child class can implement an interface:
<?php
interface water
{
public function makeItWet();
}
class weather
{
public function start()
{
return 'Here is some weather';
}
}
class rain extends weather implements water
{
public function makeItWet()
{
return 'It is wet';
}
}
$a = new rain();
echo $a->start();
echo $a->makeItWet();
?>
Another note about default values in interfaces is that an class must implement at least the arguments as in the interface. that is: an implementation may have more arguments but not less if these additional arguments have an default value and thus can be called as declared in the interface.
an litte example:
<?php
interface myInterface{
public function setStuff($id, $name);
}
class MyFirstClass implements myInterface{
public function setStuff($id, $name);
}
class MySecondClass implements myInterface{
public function setStuff($id, $name, $type);
}
class myThirdClass implements myInterface{
public function setStuff($id, $name, $type=0);
}
?>
Here mySecondClass will print an fatal error while myThirdClass is just fine because myThirdClass::setStuff($id, $name); is valid and thus fullfills the interface requirements. an interface declares as set of requirement on how methods can be called and any class implementing an interface thus agrees that is will provide these methods and that they can be called as in the interface. adding additional arguments with default values is thus allowed because it does not violate the agreement that the method can be called as in the interface.
In regards to what Hayley Watson is writing:
The "interface" is a method of enforcing that anyone who implements it must include all the functions declared in the interface. This is an abstraction method, since you cannot just declare a base class and do something like "public abstract function myTest();" and later on extend that class.
If you don't override the default value in a parameter list, it's assumed that the default value was received by time you have any control to read or relay the value on again. There should be no problem in having all or none of your parameters in an interface having a default value, as the value is "auto-filled" if not explicitly provided.
I just came across interfaces in PHP.. but I use them quite a bit in Java and Delphi. Currently building different DB wrappers, but all must enforce common access using a base class.. and also enforce that all of specific routines are implemented.
php at wallbash dot com's comment of "It's important to note this because it is very unexpected behavior and renders many common Interface completly useless" doesn't make sense.
the idea of the interface is to force objects that aren't related to be reused in a common way. without them, to force that requirement, all objects that need those methods implemented would have to be descended from a base class that's known to have those methods. that's clearly not a smart idea if these objects aren't actually related.
one example (that i'm currently working on) is a background service that pulls information down from different content providers. i have a transport and i have an import. for both, what actually happens in the background is different from provider to provider, but since i'm implementing a transport & import interface, i only need to write code once, because i know exactly the what methods will be implemented to get the job done. then, i just have a config file that loads the class dynamically. i don't need something like
if ( $provider == "some company" )
{
// use this set of code
}
elseif ( $provider == "another company" )
{
// use this other set of code
}
instead, i can do:
foreach ( $providers as $provider => $info )
{
$_transport = $info['transportObject'];
$transport = new $_transport();
$_import = $info['importObject'];
$import = new $_import();
$transport->setImporter( $import );
$transport->retrieve();
}
it is expected behavior that when a class implements two interfaces that share one or more method names, an error is thrown, because interfaces don't relate to each other. if you want that sort of inferred behavior (i.e. A and B are different except for these shared methods), stick to [abstract] classes.
it sucks that interface methods might collide for some common types of tasks (get(), set(), etc.), so knowing that, design your interfaces with more unique method names.
The structure I am working with has a lot of inheritance going on, but not all methods are specified in one place. I needed a way to make sure an interface would be used, but that the method(s) defined in the interface are defined somewhere.
As such, I learned that the parent can define the interface's methods, and then the children can override that method at will without having to worry about the interface.
To expand on nrg1981's example, the following is possible:
<?php
interface water
{
public function makeItWet();
}
class weather
{
public function makeItWet()
{
return 'it may or may not be wet';
}
public function start()
{
return 'Here is some weather';
}
}
class rain extends weather implements water
{
public function makeItWet()
{
return 'It is wet';
}
}
class thunder extends weather implements water
{
}
$a = new rain();
echo $a->start() . "\n";
echo $a->makeItWet() . "\n";
$a = new thunder();
echo $a->start() . "\n";
echo $a->makeItWet() . "\n";
?>
While a subclass may implement an interface by extending an abstract class that implements the interface, I question whether it is good design to to do so. Here's what I would suggest while taking the liberty of modifying the above weather/wet model:
<?php
interface water
{
public function makeItWet();
}
/**
* abstract class implements water but defines makeItWet
* in the most general way to allow child class to
* provide specificity
**/
abstract class weather implements water
{
private $cloudy;
public function makeItWet(){}
abstract public function start();
abstract public function getCloudy();
abstract public function setCloudy();
}
class rain extends weather {
private $cloudy;
public function start() {
return "Here's some weather. ";
}
public function makeItWet() {
return 'it is raining cats and dogs today.';
}
public function getCloudy() {
return $this->cloudy;
}
public function setCloudy($bln=false) {
$this->cloudy = $bln;
}
}
$a = new rain();
echo $a->start();
$a->setCloudy(true);
if ($a->getCloudy()) {
echo 'It is a cloudy day and ';
}
echo $a->makeItWet();
?>
In response to harryjry and mehea concerning your Weather Model. The problem is that you don't need all the things you think you need. In OOP, good class definitions get to the point rather quickly.
<?php
class Weather{
public $time, $temperature, $humidity;
public function __construct($tm, $t, $h){
$this->time = $tm;
$this->temperature = $t;
$this->humidity = $h;
}
public function __toString(){
return "Time: $this->time,
Temperature: $this->temperature°,
Humidity: $this->humidity%";
}
}
$forecasts = array(
new Weather("1:00 pm", 65, 42),
new Weather("2:00 pm", 66, 40),
new Weather("3:00 pm", 68, 39)
// add more weather reports as desired...
);
echo "Forecast for Chicago, IL:<br>";
foreach($forecasts as $forecast) echo ' - ' . $forecast '<br>';
?>
Forecast for Chicago, IL:
- Time: 1:00 pm, Temperature: 65°, Humidity: 42%
- Time: 2:00 pm, Temperature: 66°, Humidity: 40%
- Time: 3:00 pm, Temperature: 68°, Humidity: 39%
Note: MySQL can store data like this already, but if you included constants, more variables, and other functions in the Weather class, then maybe, just maybe it could be of use.
FYI, interfaces can define constructors, destructors, and magic methods. This can be very helpful especially in the case of constructors when instantiating an implementing class via reflection in some sort of factory. Of course, it is not recommended to do such a thing since it goes against the nature of a true interface.This may help understand EX.2. Below are modifiers and additions tothe code. Refer to EX.2 to make a complete code block(this saves comment
space!).
I found the function definition baz(Baz $baz) baffling. Lucky was
able to sus it out fast. Seems method baz requires just one arg and
that must be an instance of the class Baz. Here is a way to know how to
deal with that sort of arg...
<?php
# modify iface b...adding $num to get better understanding
interface b extends a
{
public function baz(Baz $baz,$num);
}
# mod claas c
class c implements b
{
public function foo()
{
echo'foo from class c';
}
public function baz(Baz $baz,$num)
{
var_dump ($baz);# object(Baz)#2 (1) { ["bb"]=> string(3) "hot" }
echo '<br>';
echo $baz->bb." $num";echo '<br>';# hot 6
}
}
# add a class Baz...
class Baz
{
public $bb='hot';
function ebaz(){
echo'this is BAZ';
}
}
# set instance of Baz and get some output...
$bazI=new Baz;
baz::ebaz();echo '<br>';# this is BAZ
c::baz($bazI,6);
?>
Interfaces can define static methods, but note that this won't make sense as you'll be using the class name and not polymorphism.
...Unless you have PHP 5.3 which supports late static binding:
<?php
interface IDoSomething {
public static function doSomething();
}
class One implements IDoSomething {
public static function doSomething() {
echo "One is doing something\n";
}
}
class Two extends One {
public static function doSomething() {
echo "Two is doing something\n";
}
}
function example(IDoSomething $doer) {
$doer::doSomething(); // "unexpected ::" in PHP 5.2
}
example(new One()); // One is doing something
example(new Two()); // Two is doing something
?>
If you have PHP 5.2 you can still declare static methods in interfaces. While you won't be able to call them via LSB, the "implements IDoSomething" can serve as a hint/reminder to other developers by saying "this class has a ::doSomething() method".
Besides, you'll be upgrading to 5.3 soon, right? Right?
(Heh. I just realized: "I do something". Unintentional, I swear!)
I was wondering if implementing interfaces will take into account inheritance. That is, can inherited methods be used to follow an interface's structure?
<?php
interface Auxiliary_Platform {
public function Weapon();
public function Health();
public function Shields();
}
class T805 implements Auxiliary_Platform {
public function Weapon() {
var_dump(__CLASS__);
}
public function Health() {
var_dump(__CLASS__ . "::" . __FUNCTION__);
}
public function Shields() {
var_dump(__CLASS__ . "->" . __FUNCTION__);
}
}
class T806 extends T805 implements Auxiliary_Platform {
public function Weapon() {
var_dump(__CLASS__);
}
public function Shields() {
var_dump(__CLASS__ . "->" . __FUNCTION__);
}
}
$T805 = new T805();
$T805->Weapon();
$T805->Health();
$T805->Shields();
echo "<hr />";
$T806 = new T806();
$T806->Weapon();
$T806->Health();
$T806->Shields();
/* Output:
string(4) "T805"
string(12) "T805::Health"
string(13) "T805->Shields"
<hr />string(4) "T806"
string(12) "T805::Health"
string(13) "T806->Shields"
*/
?>
Class T805 implements the interface Auxiliary_Platform. T806 does the same thing, but the method Health() is inherited from T805 (not the exact case, but you get the idea). PHP seems to be fine with this and everything still works fine. Do note that the rules for class inheritance doesn't change in this scenario.
If the code were to be the same, but instead T805 (or T806) DOES NOT implement Auxiliary_Platform, then it'll still work. Since T805 already follows the interface, everything that inherits T805 will also be valid. I would be careful about that. Personally, I don't consider this a bug.
This seems to work in PHP5.2.9-2, PHP5.3 and PHP5.3.1 (my current versions).
We could also do the opposite:
<?php
class T805 {
public function Weapon() {
var_dump(__CLASS__);
}
}
class T806 extends T805 implements Auxiliary_Platform {
public function Health() {
var_dump(__CLASS__ . "::" . __FUNCTION__);
}
public function Shields() {
var_dump(__CLASS__ . "->" . __FUNCTION__);
}
}
$T805 = new T805();
$T805->Weapon();
echo "<hr />";
$T806 = new T806();
$T806->Weapon();
$T806->Health();
$T806->Shields();
/* Output:
string(4) "T805"
<hr />string(4) "T805"
string(12) "T806::Health"
string(13) "T806->Shields"
*/
?>
This works as well, but the output is different. I'd be careful with this.
If you want to ensure implementation classes are correctly initialised (i.e. due to trickery one needs to do to work around lack of multiple inheritance), simply add __construct() to your interface, so risk of init being forgotten is reduced.If it isn't already obvious, you can create an object of a class above the class declaration if it does NOT implement an interface. However, when a class DOES implement an interface, PHP will throw a "class not found" error unless the instantiation declaration is _below_ the class definition.
<?php
$bar = new foo(); // Valid
class foo
{
}
?>
<?php
$bar = new foo(); // Invalid - throws fatal error
interface foo2
{
}
class bar implements foo2
{
}
$bar = new foo(); // Valid, since it is below the class declaration
?>
Also, @Jeffrey -- Lol? What? Is that a joke? PHP interfaces have nothing to do with connecting to "peripheral devices" or "cameras", etc. Not even in the least sense. This is a very common miscommunication with the word "interface", as interfaces in programming are not at all like interfaces in electronics or drivers, etc.
PHP prevents interface a contant to be overridden by a class/interface that DIRECTLY inherits it. However, further inheritance allows it. That means that interface constants are not final as mentioned in a previous comment. Is this a bug or a feature?
<?php
interface a
{
const b = 'Interface constant';
}
// Prints: Interface constant
echo a::b;
class b implements a
{
}
// This works!!!
class c extends b
{
const b = 'Class constant';
}
echo c::b;
?>
If you use namespaces and autoloading, do not forget to mention the use statement for each class used in yours arguments, before your class:
<?php
#file : fruit/squeezable.php
namespace fruit
use BarFoo;
interface squeezable {
public function squeeze (Foo $foo);
}
?>
<?php
#file: orange
namespace fruitcitrus;
class orange {
public function squeeze(Foo $foo);
}
#Will throw an exception Fatal error: Declaration of "fruit\citrus\orange::squeeze must be compatible with that of fruit\squeezable() in fruit/squeezable.php
?>
<?php
#file: orange
namespace fruitcitrus;
use BarFoo; #DO NOT FORGET THIS!
class orange {
public function squeeze (Foo $foo);
}
#Will be correct
?>
It seems like many contributors are missing the point of using an INTERFACE. An INTERFACE is not specifically provided for abstraction. That's what a CLASS is used for. Most examples in this article of interfaces could be achieved just as easily using just classes alone.
An INTERFACE is provided so you can describe a set of functions and then hide the final implementation of those functions in an implementing class. This allows you to change the IMPLEMENTATION of those functions without changing how you use it.
For example: I have a database. I want to write a class that accesses the data in my database. I define an interface like this:
interface Database {
function listOrders();
function addOrder();
function removeOrder();
...
}
Then let's say we start out using a MySQL database. So we write a class to access the MySQL database:
class MySqlDatabase implements Database {
function listOrders() {...
}
we write these methods as needed to get to the MySQL database tables. Then you can write your controller to use the interface as such:
$database = new MySqlDatabase();
foreach ($database->listOrders() as $order) {
Then let's say we decide to migrate to an Oracle database. We could write another class to get to the Oracle database as such:
class OracleDatabase implements Database {
public function listOrders() {...
}
Then - to switch our application to use the Oracle database instead of the MySQL database we only have to change ONE LINE of code:
$database = new OracleDatabase();
all other lines of code, such as:
foreach ($database->listOrders() as $order) {
will remain unchanged. The point is - the INTERFACE describes the methods that we need to access our database. It does NOT describe in any way HOW we achieve that. That's what the IMPLEMENTing class does. We can IMPLEMENT this interface as many times as we need in as many different ways as we need. We can then switch between implementations of the interface without impact to our code because the interface defines how we will use it regardless of how it actually works.
By asking your colleague to implement your interface, you are asking him to guarantee that he has implemented all the methods you need. He can implement multiple interfaces, each being a contract, so that the guy cleaning up the cruft down the road can see which methods belong to which area of concern; but since interfaces are primarily contracts rather than documentation, a class cannot implement two interfaces containing the same method since that would make the contract lose credibility through ambiguity. Thus a class can implement two interfaces with overlapping concerns only by factoring their common methods into a third interface that serves as a base for the first two, which resolves the contractual ambiguity.By asking your colleague to implement your interface, you are asking him to guarantee that he has implemented all the methods you need. He can implement multiple interfaces, each being a contract, so that the guy cleaning the cruft down the road can see which methods belong to which area of concern; but since interfaces are primarily contracts rather than documentation, a class cannot implement two interfaces containing the same method since that would make the contract lose credibility through ambiguity. Thus a class can implement two interfaces with overlapping concerns only by factoring their common methods into a third interface that serves as a base for the first two, which resolves the contractual ambiguity.Implementation must be strict, subtypes are not allowed.
"The class implementing the interface must use the EXACT SAME METHOD SIGNATURES as are defined in the interface. Not doing so will result in a fatal error. "
<?php
interface I
{
function foo(stdClass $arg);
}
class Test extends stdClass
{
}
class Implementation implements I
{
function foo(Test $arg)
{
}
}
?>
Result:
Fatal error: Declaration of InterfaceImplementation::foo() must be compatible with I::foo(stdClass $arg) in test.php on line XY
simple example :)
<?php
interface testThis
{
public function alpha();
public function beta();
}
trait setInterface
{
public function alpha()
{
echo __function__." wurde implementiert";
}
}
class b
{
public function beta()
{
echo __function__." wurde implementiert";
}
}
class a extends b implements testThis
{
use setInterface;
/*
public function alpha()
{
echo __function__." wurde implementiert";
}
public function beta()
{
echo __function__." wurde implementiert";
}
*/
public function __construct()
{
echo "wat geht? <br>";
}
}
$testInterface = new a();
$testInterface ->alpha();
echo "<br>";
$testInterface ->beta();
?>
The class implementing the interface must use the exact same method signatures as are defined in the interface. Not doing so will result in a fatal error. -- this documentation page.
But, if you use default values in arguments in methods, fatal error is not follow:
<?php
interface myInterface {
public function __construct();
}
class concret implements myInterface {
public function __construct($arg=null)
{
print_r(func_get_args());
}
}
$obj = new concret(123);
?>
Array ( [0] => 123 )
to dlovell2011 at yahoo dot com wrote:It seems like many contributors are missing the point of using an INTERFACE. An INTERFACE is not specifically provided for abstraction.
...
An INTERFACE is provided so you can describe a set of functions and then hide the final implementation of those functions in an implementing class. This allows you to change the IMPLEMENTATION of those functions without changing how you use it.
--------------
I believe the unique thing that Interfaces provide is to support the same functions in different classes that are **not descended from a common ancestor**.
Different implementations of the same functions does not need interfaces--it can be achieved through subclasses.
In their book on Design Patterns, Erich Gamma and his associates (AKA: "The Gang of Four") use the term "interface" and "abstract class" interchangeably. In working with PHP and design patterns, the interface, while clearly a "contract" of what to include in an implementation is also a helpful guide for both re-use and making changes. As long as the implemented changes follow the interface (whether it is an interface or abstract class with abstract methods), large complex programs can be safely updated without having to re-code an entire program or module.
In PHP coding with object interfaces (as a keyword) and "interfaces" in the more general context of use that includes both object interfaces and abstract classes, the purpose of "loose binding" (loosely bound objects) for ease of change and re-use is a helpful way to think about both uses of the term "interface." The focus shifts from "contractual" to "loose binding" for the purpose of cooperative development and re-use.
You can change some methods signature from interface if you pass parameters with default values. For instance:
<?php
interface Foo {
public function foo($foo);
}
class Bar implements Foo {
public function foo($foo, $bar = null) {
return $foo . $bar;
}
}
$bar = new Bar();
// output: worksfine
echo $bar->foo('works', 'fine');
Just wrote some examples of duck-typing in PHP. Sharing here.
<?php
/**
* An example of duck typing in PHP
*/
interface CanFly {
public function fly();
}
interface CanSwim {
public function swim();
}
class Bird {
public function info() {
echo "I am a {$this->name}\n";
echo "I am an bird\n";
}
}
/**
* some implementations of birds
*/
class Dove extends Bird implements CanFly {
var $name = "Dove";
public function fly() {
echo "I fly\n";
}
}
class Penguin extends Bird implements CanSwim {
var $name = "Penguin";
public function swim() {
echo "I swim\n";
}
}
class Duck extends Bird implements CanFly, CanSwim {
var $name = "Duck";
public function fly() {
echo "I fly\n";
}
public function swim() {
echo "I swim\n";
}
}
/**
* a simple function to describe a bird
*/
function describe($bird) {
if ($bird instanceof Bird) {
$bird->info();
if ($bird instanceof CanFly) {
$bird->fly();
}
if ($bird instanceof CanSwim) {
$bird->swim();
}
} else {
die("This is not a bird. I cannot describe it.");
}
}
// describe these birds please
describe(new Penguin);
echo "---\n";
describe(new Dove);
echo "---\n";
describe(new Duck);
Solution for overriding interface constants
//we can override interface constants by using abstract class
//if Test Class implements inter1 than we can not override inter1 interface constants
example:
<?php
interface inter1 {
const interface1 = "I am from interface 1";
function foo1();
function bar1();
}
interface inter2 extends inter1 {
function foo2();
function bar2();
}
interface inter3 {
function foo3();
function bar3();
}
interface inter4 {
function foo4();
function bar4();
}
abstract class AbsClass implements inter2 {
}
class Test extends AbsClass implements inter3, inter4 {
const interface1 = "I am from test class";
public function foo1() {
}
public function foo2() {
}
public function foo3() {
}
public function foo4() {
}
public function bar1() {
}
public function bar2() {
}
public function bar3() {
}
public function bar4() {
}
public function display() {
echo inter1::interface1;
echo PHP_EOL;
echo Test::interface1;
}
}
$Obj = new Test();
$Obj->display(); //I am from interface 1 \n I am from test class
php inheritance interfaces on function/methods type declarations:
<?php
interface iInvokable {
function __invoke($arg = null);
}
interface iResponder extends iInvokable {
/** Bind next responder */
function then(iInvokable $responder);
}
class Responder implements iResponder {
function __invoke($arg = null)
{
// TODO: Implement __invoke() method.
}
/** Bind next responder */
function then(iInvokable $responder)
{
// TODO: Implement then() method.
}
}
class OtherResponder implements iResponder {
function __invoke($arg = null)
{
// TODO: Implement __invoke() method.
}
/** Bind next responder */
function then(iInvokable $responder)
{
// TODO: Implement then() method.
}
}
class Invokable implements iInvokable {
function __invoke($arg = null)
{
// TODO: Implement __invoke() method.
}
}
$responder = new Responder();
$responder->then(new OtherResponder());
$responder->then(new Invokable());
?>
<?php
interface ClassThatCanBuild
{ }
interface SpecificClass extends ClassThatCanBuild
{ }
Class MySpecificClass implements SpecificClass
{ }
interface BuilderInterface
{
function build(ClassThatCanBuild $container);
function weCanHaveMethods();
}
interface SpecificBuilderInterface extends BuilderInterface
{
/**
* (!!) this class want to allow just for build
* specific classes.
* i`m still on the rule with MySpecificClass
* because extend from ClassThatCanBuild
* but php don`t allow it at all
*
* "" declaration of must be compatible with
* interface of BuilderInterface->build ""
*
* @param \MySpecificClass $container
*/
function build(MySpecificClass $container);
}
?>