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 can be used to add CSS styles directly in the HTML tag?
type style class
<div style="width: 80%; border: 3px solid #888888;">Content</div>
Which CSS transform method distorts the HTML element in a given angle (including its content)?
translate() scale() skew()
#some_id {
  transform: skew(20deg, 25deg);
  -ms-transform: skew(20deg, 25deg);   /* IE 9 */
  -webkit-transform: skew(20deg, 25deg);   /* Safari and Chrome */
}
Click on the function which converts a Date object to a string.
indexOf() toString() getDate()
var rightnow = new Date();
alert( rightnow.toString() );
Which function applies a callback function to the elements of the given array?
array_merge() array_search() array_map()
$arr = arra("abc", "<p>xyz</p>", "<em>PHP</em>");
// apply the strip_tags() function to delete HTML tags from each array item
$arr = array_map("strip_tags", $arr);
}
PHP OOP - Final Classes and Methods

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