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
What attribute makes the input text box to not be modified by the user?
checked="checked" readonly="readonly" disabled="disabled"<input type="text" value="fixed-value" readonly="readonly" name="a_name" />
What CSS property allows you to create rounded corners in your webpage design?
background-size border-size border-radius.class {
border:2px solid blue;
border-radius:1.2em;
}What instruction displays a confirmation dialog box to the viewer, who must then click OK or Cancel to proceed?
indexOf() confirm() prompt()var ques = window.confirm("The result of 0+0 is 0?");
if (ques) alert("Corect");
else alert("Incorrect");Indicate the PHP function that returns the lowest number of the parameter values.
floor() ceil() min()$min_nr = min(12, 8, 25, 13);
echo $min_nr; // 8