What is abstract Classes

As from name it seem like something that is hidden. Yes nature of the abstract classes are same. Abstract classes are those classes which can not be directly initialized. Or in other word we can say that you can not create object of abstract classes. Abstract classes always created for inheritance purpose. You can only inherit abstract class in your child class. Lots of people say that in abstract class at least your one method should be abstract. Abstract method are the method which is only defined but declared. This is not true definition as per my assumption. But your any class has at least one method abstract than your class is abstract class.

Usually, an abstract class is also known as base class. We call it base class because the abstract class is not the class which is available directly for creating an object. It can only act as the parent class of any normal class. You can use an abstract class in the class hierarchy. Mean one abstract class can inherit another abstract class also.

Abstract classes in PHP

Abstract classes in PHP are similar like other oop languages. You can create abstract classes in PHP using abstract keyword. Once you will make any class abstract in PHP you can not create an object of that class.
abstract class abc
{
public function xyz()
{
return 1;
}
}
$a = new abc();//this will throw error in php

above code will throw an error in PHP.

Abstract classes in PHP are only for inheriting in other class.
abstract class testParent
{
public function abc()
{
//body of your funciton
}
}
class testChild extends testParent
{
public function xyz()
{
//body of your function
}
}
$a = new testChild();

In above example, you are creating of testChild Class. TestChild class is inheriting testParent abstract class. So your abstract class is only available for inheritance. The main motive of creating abstract classes in PHP is to apply restriction of direct initialization or object creation.

Implementation of abstract method

As we know that abstract functions are those functions of abstract class which is only defined. It will be declared in your child class. You can create any method abstract using keyword abstract. You can only create abstract method either in abstract class or interface. Following is example of the abstract method implementation:

abstract class abc
{
abstract protected function f1($a , $b);
}
class xyz extends abc
{
protected function f1($name , $address)
{
echo "$name , $address";
}
}
$a = new xyz();

In class abc we have defined an abstract function f1. Now when we have inherited class abc then declared function f1. If you have an abstract method in your abstract class then once you inherit your abstract class then it is necessary to declare your abstract method. If you will not declare your abstract method then PHP will throw error in that case.

You can declare your abstract method in child class with the same visibility or less restricted visibility.

abstract class parentTest
{
abstract protected function f1();
abstract public function f2();
//abstract private function f3(); //this will trhow error
}
class childTest
{
public function f1()
{
//body of your function
}
public function f2()
{
//body of your function
}
protected function f3()
{
//body of your function
}
}
$a = new childTest();

In above code, you can see that you have declared 3 functions in the abstract class. But the private declaration of the abstract method will always throw an error. Because the private method is availabe only in the same class context. But in the case of f1. This is protected. Now in the child class, we have defined it as public because public is less restricted than protected. And for function f2 which is already public so we have defined it as public in our child class. We have defined it public because no any visibility is less restricted than public.

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