PHP OOP - Final Classes and Methods

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.

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Daily Test with Code Example

HTML

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PHP-MySQL

Which HTML5 tag defines marked text? (can be used to highlight parts of text)

<p>Free corses: <mark>coursesweb.net</mark> for Web Development.</p>

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:focus :hover :active

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toPrecision(x) toFixed(x) floor(x)

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num = num.toFixed(2);
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Indicate the PHP function which reads an entire file into an array.

[) file() readfile()

$arr = file("a_file.txt", FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
var_export($arr);

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