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 is used in <img> tag for the address of the image?
href src rel
<img src="http://coursesweb.net/imgs/webcourses.gif" width="191" height="63" alt="Courses-Web" />
Which CSS code hides the element on page?
display: none; display: inline; position: relative;
#id {
  display: none;
}
What instruction stops the execution of a while() or for() statement?
continue prompt() break
for(var i = 0; i< 8; i++) {
  if(i > 1) break;
  alert(i);
}
Indicate the function that can create a constant.
define() include() defined()
define("CONSTANT_NAME", "value");
echo CONSTANT_NAME;
PHP OOP - Final Classes and Methods

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