Here's an example that helped me with understanding abstract classes. It's just a very simple way of explaining it (in my opinion). Lets say we have the following code:
<?php
class Fruit {
private $color;
public function eat() {
}
public function setColor($c) {
$this->color = $c;
}
}
class Apple extends Fruit {
public function eat() {
}
}
class Orange extends Fruit {
public function eat() {
}
}
?>
Now I give you an apple and you eat it.
<?php
$apple = new Apple();
$apple->eat();
?>
What does it taste like? It tastes like an apple. Now I give you a fruit.
<?php
$fruit = new Fruit();
$fruit->eat();
?>
What does that taste like??? Well, it doesn't make much sense, so you shouldn't be able to do that. This is accomplished by making the Fruit class abstract as well as the eat method inside of it.
<?php
abstract class Fruit {
private $color;
abstract public function eat();
public function setColor($c) {
$this->color = $c;
}
}
?>
Now just think about a Database class where MySQL and PostgreSQL extend it. Also, a note. An abstract class is just like an interface, but you can define methods in an abstract class whereas in an interface they are all abstract.
