Abstract Classes and Methods

An abstract class is a class that contains at least one abstract method. An abstract method is a method that is declared, but not implemented in the code. An abstract class or method is defined with the abstract keyword:

abstract class ParentClass {
  abstract public function someMethod1();
  abstract public function someMethod2($name, $color);
  abstract public function someMethod3() : string;
}

when a child class is inherited from an abstract class, we have the following rules:
1. The child class method must be defined with the same name and it redeclares the parent abstract method
2. The child class method must be defined with the same or a less restricted access modifier
The number of required arguments must be the same. However, the child class may have optional arguments in addition