Final classes
Inheritance allows for enormous flexibility within a class hierarchy. You can create subclasses to extend the functionality of a base class, but PHP OOP gives the posibility to create classes that cannot be extended. Such a class is called
final class.
A
final class is declared by adding the
final keyword before the
class word.
- For example:
<?php
// base class (declared final)
final class Base {
// ... PHP code
}
// define a child class derivated from Base
class BaseChild extends Base {
// ... PHP instructions
}
?>
Running this code will generate the following error:
Fatal error: Class BaseChild may not inherit from final class (Base) in ...
Final methods
A normal method (public or protected) can be overridden in the child class. If you want a method to remain fixed and unchanging, prefix the definition with the
final keyword.
A final method cannot be overridden.
- For example:
<?php
// base class
class Base {
// final method
final public function testMethod() {
echo 'This is a final method';
}
}
// define a child class derivated from Base
class BaseChild extends Base {
// override the testMethod()
public function testMethod() {
echo 'Another text';
}
}
?>
This example will generate the following error:
Fatal error: Cannot override final method Base::testMethod() in ...
By declaring a class or method final, you limit the flexibility given by inheritance, so, use final with care.
Daily Test with Code Example
HTML
CSS
JavaScript
PHP-MySQL
Which tag defines the clickable areas inside the image map?
<map> <img> <area><img src="image.jpg" usemap="#map1">
<map name="map1">
<area shape="rect" coords="9, 120, 56, 149" href="#">
<area shape="rect" coords="100, 200, 156, 249" href="#">
</map>
Which CSS property defines what is done if the content in a box is too big for its defined space?
display overflow position#id {
overflow: auto;
}
Click on the event which is triggered when the mouse is positioned over an object.
onclick onmouseover onmouseoutdocument.getElementById("id").onmouseover = function(){
document.write("Have Good Life");
}
Indicate the PHP variable that contains data added in URL address after the "?" character.
$_SESSION $_GET $_POSTif(isset($_GET["id"])) {
echo $_GET["id"];
}