Class Abstraction

PHP has abstract classes and methods. Classes defined as abstract cannot 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 class, and follow the usual inheritance and signature compatibility rules.

Example #1 Abstract class example

<?php
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 above example will output:

ConcreteClass1
FOO_ConcreteClass1
ConcreteClass2
FOO_ConcreteClass2

Example #2 Abstract class example

<?php
abstract class AbstractClass
{
// Our abstract method only needs to define the required arguments
abstract protected function prefixName($name);

}

class
ConcreteClass extends AbstractClass
{

// Our child class may define optional arguments not in the parent's signature
public function prefixName($name, $separator = ".") {
if (
$name == "Pacman") {
$prefix = "Mr";
} elseif (
$name == "Pacwoman") {
$prefix = "Mrs";
} else {
$prefix = "";
}
return
"{$prefix}{$separator} {$name}";
}
}

$class = new ConcreteClass;
echo
$class->prefixName("Pacman"), "\n";
echo
$class->prefixName("Pacwoman"), "\n";
?>

The above example will output:

Mr. Pacman
Mrs. Pacwoman