PHP Abstract Class

Introcution

In order to understand abstract classes you should know 4 topics:

1. class
2. inheritance
3. interface
4. access modifiers

We have already talked about those topics in other posts so by know you should know them.

What is an abstract class

Well simply put, an abstract class is like an interface so it has methods that are only defined and not implemented but at the same time it’s like a class and can have methods that are implemented.

It’s like having the best of both worlds

Let’s see an example

<?php
abstract class Human
{
    private $name;
    
    public function __construct(string $name)
    {
        $this->name = $name;
    }
    
    public function sayHello()
    {
        echo 'Hello my name is '.$this->name;
    }
    
    abstract protected function nationality();
}

abstract class vs class

As you can see the difference with a class is that it has the word abstract in the name. Abstract class. And for the methods that are going to be defined only and not implemented we should use the same keyword. Abstract public/protected function.

Let’s see an example of a class that extends this abstract class and implement it.

class Pratham extends Human {
    
    public function nationality()
    {
        echo "I am from India";
    }
}

$pratham = new Pratham('Pratham');
$pratham->sayHello();
// Hello my name is Pratham
$pratham->nationality();
// I am from India

access modifiers in an abstract class

Do you see how the abstract class is protected but when we implement it, we made it public?

If the abstract method is protected the implemented method can be protected or public but if the abstract method is public then the implemented method must be public as well.

abstract class vs interface

Let’s compare our abstract class with an interface.

There are 4 main differences.

1. abstract classes can have properties and as you have seen we had name in the abstract class. We can’t have properties in an interface.
2. As you have seen, we had an abstract method that was protected. In an interface all the methods must be public.
3. you cannot implement a method inside an interface but as you can see we have implemented the sayHello method in our abstract class.
4. if your class wants to implement the methods of an interface you should use implements but for abstract class we use extends

let's take a look at it again

<?php
abstract class Human
{
    private $name;
    
    public function __construct(string $name)
    {
        $this->name = $name;
    }
    
    public function sayHello()
    {
        echo 'Hello my name is '.$this->name;
    }
    
    abstract protected function nationality();
}

class Pratham extends Human {
    
    public function nationality()
    {
        echo "I am from India";
    }
}

$pratham = new Pratham('Pratham');
$pratham->sayHello();
// Hello my name is Pratham
$pratham->nationality();
// I am from India

Conclusion

Now you know about abstract classes in PHP.

I recommend you to open a PHP files and try writing an abstract class. add abstract methods to it and try to extend it and implement its abstract methods.

If you have any suggestions, questions, or opinions, please contact me. I’m looking forward to hearing from you!

Key takeaways

• define an abstract class
• abstract class vs class
• abstract class vs interface
• abstract methods
• access modifiers in an abstract class