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:
// 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:
// 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

Which tag is used in <table> to create table header cell?
<thead> <th> <td>
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Which CSS property sets the distance between lines?
line-height word-spacing margin
.some_class {
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Which function opens a new browser window.
alert() confirm() open()
document.getElementById("id_button").onclick = function(){"");
Indicate the PHP function that returns an array with names of the files and folders inside a directory.
mkdir() scandir() readdir()
$ar_dir = scandir("dir_name");
PHP OOP - Final Classes and Methods

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