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 attribute specifies the URL address where to send the form-data?
method action name<form action="script.php" method="post"> ... </form>
Which CSS property can be used to break lines in the middle of words?
word-wrap line-height font-size#id {
width: 100px;
word-wrap: break-word;
}Which function sorts the elements of an array into alphabetical order, based on the string values?
pop() sort() shift()var tutorials = ["php", "html", "css", "flash"];
tutorials.sort();
alert(tutorials[0]); // css
Indicate the function that returns the value of the last element into an array.
current() next() end()$code =[10=>"Perl", 20=>"PHP", 21=>"Python", 30=>"JavaScript");
$last = end($code);
echo $last; // JavaScript