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 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"];
alert(tutorials[0]);          // css
Indicate the function that returns the value of the last element into an array.
current() next() end()
$code = array(10=>"Perl", 20=>"PHP", 21=>"Python", 30=>"JavaScript");
$last = end($code);
echo $last;      // JavaScript
PHP OOP - Final Classes and Methods

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