interface
Object interfaces allow you to create code which specifies which methods a class must implement, without having to define how these methods are handled.
Interfaces are defined in the same way as a class, but with the interface keyword replacing the class keyword and without any of the methods having their contents defined.
All methods declared in an interface must be public; this is the nature of an interface.
Note that it is possible to declare a constructor in an interface, what can be useful in some contexts, e.g. for use by factories.
implements
To implement an interface, the implements operator is used. All methods in the interface must be implemented within a class; failure to do so will result in a fatal error. Classes may implement more than one interface if desired by separating each interface with a comma.
Note: Prior to PHP 5.3.9, a class could not implement two interfaces that specified a method with the same name, since it would cause ambiguity. More recent versions of PHP allow this as long as the duplicate methods have the same signature.
Note: Interfaces can be extended like classes using the extends operator.
Note: 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.
Constants
It's possible for interfaces to have constants. Interface constants works exactly like class constants except they cannot be overridden by a class/interface that inherits them.
Examples
Example #1 Interface example
<?php
//?Declare?the?interface?'iTemplate'
interface?iTemplate
{
????public?function?setVariable($name,?$var);
????public?function?getHtml($template);
}
//?Implement?the?interface
//?This?will?work
class?Template?implements?iTemplate
{
????private?$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;
????}
}
//?This?will?not?work
//?Fatal?error:?Class?BadTemplate?contains?1?abstract?methods
//?and?must?therefore?be?declared?abstract?(iTemplate::getHtml)
class?BadTemplate?implements?iTemplate
{
????private?$vars?=?array();
??
????public?function?setVariable($name,?$var)
????{
????????$this->vars[$name]?=?$var;
????}
}
?>Example #2 Extendable Interfaces
<?php
interface?a
{
????public?function?foo();
}
interface?b?extends?a
{
????public?function?baz(Baz?$baz);
}
//?This?will?work
class?c?implements?b
{
????public?function?foo()
????{
????}
????public?function?baz(Baz?$baz)
????{
????}
}
//?This?will?not?work?and?result?in?a?fatal?error
class?d?implements?b
{
????public?function?foo()
????{
????}
????public?function?baz(Foo?$foo)
????{
????}
}
?>Example #3 Multiple interface inheritance
<?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()
????{
????}
}
?>Example #4 Interfaces with constants
<?php
interface?a
{
????const?b?=?'Interface?constant';
}
//?Prints:?Interface?constant
echo?a::b;
//?This?will?however?not?work?because?it's?not?allowed?to?
//?override?constants.
class?b?implements?a
{
????const?b?=?'Class?constant';
}
?>An interface, together with type-hinting, provides a good way to make sure that a particular object contains particular methods. See instanceof operator and type hinting.
← Class Abstraction
Traits →
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