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 HTML5 tag is indicated to be used as container for menu with navigation links in Web site?
<section> <nav> <article><nav><ul>
<li><a href="http://coursesweb.net/css/" title="CSS Course">CSS Course</a></li>
<li><a href="http://www.marplo.net/jocuri/" title="Flash Games">Flash Games</a></li>
</ul></nav>
Which CSS property shifts an item horizontally to the left or right of where it was?
text-align clear float.some_class {
width: 30%;
float: left;
}Click on the Math object method which returns x, rounded downwards to the nearest integer.
Math.ceil(x) Math.abs(x) Math.floor(x)var num = 12.34567;
num = Math.floor(num);
alert(num); // 12
Indicate the PHP function which returns the number of characters in string.
mb_strlen() count() stristr()$str = "string with utf-8 chars åèö";
$nrchr = mb_strlen($str);
echo $nrchr; // 30