So far, all the properties and methods defined in our Book class were tagged as public. That means that they are accessible to anyone, or more precisely, from anywhere. This is called the visibility
of the property or method, and there are three types of visibility. In the order of being more restrictive to less, they are as follows:
private: This type allows access only to members of the same class. If A and B are instances of the class C, A can access the properties and methods of B.protected: This type allows access to members of the same class and instances from classes that inherit from that one only. You will see inheritance in the next section.public: This type refers to a property or method that is accessible from anywhere. Any classes or code in general from outside the class can access it.
In order to show some examples, let's first create a second class in our application. Save this into a Customer.php file:
<?php
class Customer {
private...