[OOP Abstract Classes] Abstract Classes, Part 1 - Abstracting Behavior

00-Taxonomy.php

<?php

abstract class Taxonomy
{
  
  private $taxonomyName;
  
  private $taxonomySlug;
  
  public function __construct($name) {
    $this->taxonomyName = $name;
    $this->taxonomySlug = strtolower(str_ireplace(' ', '-', $this->taxonomyName));
  }
  
  public function getName() {
    return $this->taxonomyName;
  }
  
  public function getSlug() {
    return $this->taxonomySlug;
  }

  abstract protected function isHierarchical();
  abstract protected function isCategory();
  abstract protected function isTag();
  
}

01-Tag.php

<?php

class Tag extends Taxonomy
{
  protected function isHierarchical() {
    return false;
  }

  protected function isCategory() {
    return $this->isHierarchical;
  }

  protected function isTag() {
    return !$this->isHierarchical;
  }
}

02-Category.php

<?php
class Category extends Taxonomy
{
  private $parentId = -1;

  protected function isHierarchical() {
    return true;
  }

  protected function isCategory() {
    return $this->isHierarchical;
  }

  protected function isTag() {
    return !$this->isHierarchical;
  }

  public function setParentId($parentId) {
    $this->parentId = $parentId;
  }

  public function getParentId() {
    return $this->parentId;
  }
}

03-Demo.php

<?php

abstract class Taxonomy
{
  private $taxonomyName;

  private $taxonomySlug;

  public function __construct($name) {
    $this->taxonomyName = $name;
    $this->taxonomySlug = strtolower(str_ireplace(' ', '-', $this->taxonomyName));
  }

  public function getName() {
    return $this->taxonomyName;
  }

  public function getSlug() {
    return $this->taxonomySlug;
  }

  abstract protected function isHierarchical();
  abstract protected function isCategory();
  abstract protected function isTag();

}

/*--*/

class Tag extends Taxonomy
{
  protected function isHierarchical() {
    return false;
  }

  protected function isCategory() {
    return $this->isHierarchical;
  }

  protected function isTag() {
    return !$this->isHierarchical;
  }
}

/*--*/

class Category extends Taxonomy
{
  private $parentId = -1;

  protected function isHierarchical() {
    return true;
  }

  protected function isCategory() {
    return $this->isHierarchical;
  }

  protected function isTag() {
    return !$this->isHierarchical;
  }

  public function setParentId($parentId) {
    $this->parentId = $parentId;
  }

  public function getParentId() {
    return $this->parentId;
  }
}

/*- Tag Demo ----------------------------*/

$tag = new Tag('Acme Tag');
echo $tag->getName();
echo $tag->getSlug();

/*- Category Demo -----------------------*/

$category = new Category('Acme Category');

echo $category->getName();
echo $category->getSlug();
echo $category->getParentId();

$category->setParentId(100);
echo $category->getparentId();