Class Abstraction
PHP 5 introduces abstract classes and methods. Classes defined as
abstract may not be instantiated, and 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 a less restricted)
visibility. For example,
if the abstract method is defined as protected, the function implementation
must be defined as either protected or public, but not private. Furthermore
the signatures of the methods must match, i.e. the type hints and the number
of required arguments must be the same. For example, if the child class
defines an optional argument, where the abstract method's signature does
not, there is no conflict in the signature. This also applies to constructors
as of PHP 5.4. Before 5.4 constructor signatures could differ.
Abstract class example
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";
?>
]]>
&example.outputs;
Abstract class example
prefixName("Pacman"), "\n";
echo $class->prefixName("Pacwoman"), "\n";
?>
]]>
&example.outputs;
Old code that has no user-defined classes or functions named
'abstract' should run without modifications.