奋斗足迹|崔玉松

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 using the interface keyword, in the same way as a standard class, but 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.

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.

Interface example

// 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;
}
}

See also the instanceof operator.

PHP 5 introduces abstract classes and methods. It is not allowed to create an instance of a class that has been defined as abstract. Any class that contains at least one abstract method must also be abstract. Methods defined as abstract simply declare the method’s signature they cannot define the implementation.

When inheriting from an abstract class, all methods marked abstract in the parent’s class declaration must be defined by the child; additionally, these methods must be defined with the same (or weaker) visibillity. For example, if the abstract method is defined as protected, the function implementation must be defined as either protected or public.

Abstract class example

abstract class AbstractClass
{
// Force Extending class to define this method
abstract protected function getValue();
abstract protected function prefixValue($prefix);

// Common method
public function printOut() {
print $this->getValue() . “n”;
}
}

class ConcreteClass1 extends AbstractClass
{
protected function getValue() {
return “ConcreteClass1″;
}

public function prefixValue($prefix) {
return “{$prefix}ConcreteClass1″;
}
}

class ConcreteClass2 extends AbstractClass
{
public function getValue() {
return “ConcreteClass2″;
}

public function prefixValue($prefix) {
return “{$prefix}ConcreteClass2″;
}
}

$class1 = new ConcreteClass1;
$class1->printOut();
echo $class1->prefixValue(’FOO_’) .”n”;

$class2 = new ConcreteClass2;
$class2->printOut();
echo $class2->prefixValue(’FOO_’) .”n”;
?>

The example will output

ConcreteClass1
FOO_ConcreteClass1
ConcreteClass2
FOO_ConcreteClass2

Old code that has no user-defined classes or functions named ‘abstract’ should run without modifications.

The Scope Resolution Operator (also called Paamayim Nekudotayim) or in simpler terms, the double colon, is a token that allows access to static, constant, and overridden members or methods of a class.

When referencing these items from outside the class definition, use the name of the class.

Paamayim Nekudotayim would, at first, seem like a strange choice for naming a double-colon. However, while writing the Zend Engine 0.5 (which powers PHP 3), that’s what the Zend team decided to call it. It actually does mean double-colon – in Hebrew!

class MyClass {
const CONST_VALUE = 'A constant value';
}

echo MyClass::CONST_VALUE;
?>

Two special keywords self and parent are used to access members or methods from inside the class definition. Calling a parent’s method

class MyClass
{
protected function myFunc() {
echo "MyClass::myFunc()n";
}
}

class OtherClass extends MyClass
{
// Override parent's definition
public function myFunc()
{
// But still call the parent function
parent::myFunc();
echo "OtherClass::myFunc()n";
}
}

$class = new OtherClass();
$class->myFunc();
?>