PHP, Structures and Functions, ArrayObjects

ABSTRACT CLASSES & METHODS

When inheriting from an abstract class, the child class method must be defined with the same name, and the same or a less restricted access modifier.

So, if the abstract method is defined as protected, the child class method must be defined as either protected or public, but not private.

Also, the type and number of required arguments must be the same. However, the child classes may have optional arguments in addition.

So, when a child class is inherited from an abstract class, we have the following rules:

1. The child class method must be defined with the same name and it redeclares the parent abstract method.

2. The child class method must be defined with the same or a less restricted access modifier.

3. The number of required arguments must be the same. However, the child class may has optional arguments in addition.


<?php

abstract class ParentClass {
    
  abstract public function someMethod1();
  abstract public function someMethod2($name, $behavior);
  abstract public function someMethod3() : string;
  
}

?>

EXERCISE


<?php

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - 

   Parent class
   
   - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

abstract class Dwarfs {
  public $name;
  public function __construct($name) {
    $this->name = $name;
  }
  abstract public function intro() : string;
}

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - 

   Child classes
   
   - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
   
class Doc extends Dwarfs {
  public function intro() : string {
    return "$this->name<br>Leader of the group, not too good at speaking.";
  }
}

class Bashful extends Dwarfs {
  public function intro() : string {
    return "$this->name<br>The shy one.";
  }
}

class Grumpy extends Dwarfs {
  public function intro() : string {
    return "$this->name<br>Always annoyed and irritated, doesn't 
    like Snow White.";
  }
}

class Happy extends Dwarfs {
  public function intro() : string {
    return "$this->name<br>Fat, jolly, friendly, spreading joy to everyone.";
  }
}

class Sleepy extends Dwarfs {
  public function intro() : string {
    return "$this->name<br>Always tired, most observant.";
  }
}

class Dopey extends Dwarfs {
  public function intro() : string {
    return "$this->name<br>Annoying, silly, the comic relief.";
  }
}

class Sneezy extends Dwarfs {
  public function intro() : string {
    return "$this->name<br>Likes to have fun, has never 
    ending case of hay fever that makes him sneeze.";
  }
}

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 

   Create objects from the child classes
   
   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
   
$Doc = new Doc("Doc");
echo $Doc->intro();
echo "<br><br>";

$Bashful = new Bashful("Bashful");
echo $Bashful->intro();
echo "<br><br>";

$Grumpy = new Grumpy("Grumpy");
echo $Grumpy->intro();
echo "<br><br>";

$Happy = new Happy("Happy");
echo $Happy->intro();
echo "<br><br>";

$Sleepy = new Sleepy("Sleepy");
echo $Sleepy->intro();
echo "<br><br>";

$Dopey = new Dopey("Dopey");
echo $Dopey->intro();
echo "<br><br>";

$Sneezy = new Sneezy("Sneezy");
echo $Sneezy->intro();

?>

RESULT

Doc
Leader of the group, not too good at speaking.

Bashful
The shy one.

Grumpy
Always annoyed and irritated, doesn't like Snow White.

Happy
Fat, jolly, friendly, spreading joy to everyone.

Sleepy
Always tired, most observant.

Dopey
Annoying, silly, the comic relief.

Sneezy
Likes to have fun, has never ending case of hay fever that makes him sneeze.

EXERCISE


<?php

abstract class Dwarfs {

abstract protected function addName($name);
}

class ChildDwarfsClass extends Dwarfs {
    
  public function addName($name) {
    if ($name == "Peter Diklage") {
      $add = "Mr.";
    } elseif ($name == "Erica Schmidt") {
      $add = " married with Mrs.";
    } else {
      $add = "";
    }
    return "{$add} {$name}";
  }
}

$class = new ChildDwarfsClass;
echo $class->addName("Peter Diklage");
echo $class->addName("Erica Schmidt");
echo '.';

?>