Интерфейсы объектов

Интерфейсы объектов позволяют программисту 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. Для включения интерфейса в класс программист должен использовать ключевое слово "implements" и описать функционал методов, перечисленных во включаемом интерфейсе. Если это требуется, классы могут включать более одного интерфейса путём их перечисления через пробел.

Если класс включает какой-либо интерфейс и не описывает функционал всех методов этого интерфейса, выполнение кода с использованием такого класса завершится фатальной ошибкой, сообщающей, какие именно методы не были описаны.

Пример 19-18. Пример интерфейса

<?php
interface ITemplate
{
  public function setVariable($name, $var);
  public function getHtml($template);
}

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;
  }
}
?>


Интерфейсы объектов
Grigori Kochanov
17-Jul-2006 02:24
The engine does not recognise the class that implements an interface as declared in the code written before the class declaration is placed.
This means that you can't place the declaration of a classes that implements an interfaces in the code beneath the creation of an instance.

Tony2001 said this is an expected behaviour of Zend engine.

Back to PHP 3 ;-)

<?php
var_dump(class_exists('validatorCheck'));
//you don't write $obj = new validatorCheck() here

class validatorCheck implements ArrayAccess {

function offsetGet($key){}
function offsetSet($key, $value) {}
function offsetUnset($key) {}
function offsetExists($offset) {}

//class end
}

var_dump(class_exists('validatorCheck'));
//an instance can be created only here
?>

Result:

bool(false)
bool(true)
spiritus.canis at gmail dot com
25-Oct-2005 10:45
Regarding the example by cyrille.berliat:

This is not a problem and is consistent with other languages.  You'd just want to use inheritance like so:

<?php

class AbstractClass {
   public function __ToString ( ) { return 'Here I am'; }
}

class DescendantClass extends AbstractClass {}

interface MyInterface {
   public function Hello ( AbstractClass $obj );
}

class MyClassOne implements MyInterface {

   public function Hello ( AbstractClass $obj ) {
       echo $obj;
   }
} // Will work as Interface Satisfied

$myDC = new DescendantClass() ;
MyClassOne::Hello( $myDC ) ;

?>
cyrille.berliat[no spam]free.fr
17-Oct-2005 02:29
Interfaces and Type Hinting can be used but not with Inherintance in the same time :

<?

class AbstractClass
{
   public function __ToString ( ) { return 'Here I\'m I'; }
}

class DescendantClass extends AbstractClass
{

}

interface MyI
{
   public function Hello ( AbstractClass $obj );
}

class MyClassOne implements MyI
{
   public function Hello ( AbstractClass $obj )
   {
       echo $obj;
   }
} // Will work as Interface Satisfied

class MyClassTwo implements MyI
{
   public function Hello ( DescendantClass $obj )
   {
       echo $obj;
   }
} // Will output a fatal error because Interfaces don't support Inherintance in TypeHinting

//Fatal error: Declaration of MyClassTwo::hello() must be compatible with that of MyI::hello()

?>

Something a little bit bad in PHP 5.0.4 :)
nuying117 at 163 dot com
13-Oct-2005 01:48
If a class implements two interfaces , but these two interfaces have a same method,for example
<?php
interface TestInterface1
{
   function testMethod1();
   function testMethod2();
}
interface TestInterface2
{
   function testMethod2();
   function testMethod3();
   function testMethod4();
}
class ImplementClass implements TestInterface1,TestInterface2
{
   function __construct()
   {
       echo "I am constructor\r\n";
   }

   function __destruct()
   {
       echo "I am destructor\r\n";
   }

   function testMethod1()
   {}
   function testMethod2()
   {}
   function testMethod3()
   {}
   function testMethod4()
   {}
}
?>
It will cause  a fatal error!
darealremco at msn dot com
02-Oct-2005 12:53
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.
warhog at warhog dot net
11-Aug-2005 08:35
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.
marcus at synchromedia dot co dot uk
28-Jul-2005 04:11
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.
tobias_demuth at web dot de
04-May-2005 02:21
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
Sebastian Mendel
11-Mar-2005 05:12
also see: class_implements()
at: manual/en/function.class-implements.php
erik dot zoltan at msn dot com
25-Feb-2005 10:43
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.
mat.wilmots (at) wanadoo (dot) fr
20-Jan-2005 06:22
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)
m.kurzyna AT nius waw pl
23-Dec-2004 06:04
You can have a class implementing two or more interfaces, just seperate them with a coma:

<?php

interface i_one {
public one();
}

interface i_two {
public two();
}

class oneANDtwo implements i_one, i_two {
public one() {}
public two() {}
}

?>

Of course all implemented interfaces will be tested, so one needs to have one() and two() in their class to avoid errors.
russ dot collier at gmail dot com
28-Nov-2004 10:24
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

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 Last updated: Tue, 15 Nov 2005