Here we will learn about the abstract classes and methods. When we define a classes as an abstract then we have to follow the below rules:

1- We can not create an object of this abstract class.
2- The class becomes abstract if the class contains at least one abstract method.
3- Abstract methods are only declared and not defined.
4- All abstract methods declared in the parent class must be defined by the child class.
5- And the visibility of the abstract method must be equal or less than that in parent class when
defined by the child class.

Example:

abstract class MainClass
{

    abstract protected function xyz(); //This class must be defined in the child class when extended    
    abstract protected function abc($g); //This class must be defined in the child class when extended

    // This method is the common method for parent and child
    public function Display()
    {
      print  $this->xyz();
    }
}

class subClass extends MainClass
{
    protected function xyz() {
        return "abstract method xyz() is mandatory to define in the child class as it is abstract method/ class";
    }

    // the visibility of abc method is less restricted than in the parent class
    public function abc($g) {
        echo "{$g} this method is also abstract method ";
    }
}


$sbclass = new subClass();
$sbclass->Display();
$sbclass->abc('<br> Hello there') ;

OUTPUT:

abstract method xyz() is mandatory to define in the child class as it is abstract method/class
Hello there.. this method is also abstract method