Visibility

Public

Class members declared public can be accessed everywhere.

Protected

Members declared protected can be accessed only within the class itself and by inherited classes.

Private

Members declared as private may only be accessed by the class that defines the member.

Note

variables & functions are public by default

By default If declared using var, the property will be defined as public. Contrary to the OOPS Pradigms of Data Hiding

By default if declared without using visibility its declared as public function. This is in accordance with OOPS Pradigms methods are always public

Example:

<?php
    class Car{

        //Properties, by default its public
        var $color = 'green';

        // You can declare public prop. like this also
        public  $price  = 1000000;

        // Private
        private $engine = 'blah blah';

        // Protected available to Car Class, and all Sub Classes.
        protected $no_of_wheels = 4 ;

        //Method, by default its public
        function drive(){
            // Accisible only within the class function's code.
            echo 'Engine : ' . $this->engine;
            echo 'driving...';
        }

        // Private method to apply Airbag when accidents happen.
        private function openAirBag(){
            echo 'Openning Airbag for Emergency....';
        }
    }

    class TeslaCar extends Car {

        //Prop has $color, $price, $brand along with manufacturer
        public $manufacturer = 'Elon Musk';

        //Methods has drive() and selfdrive()
        function selfdrive(){
            echo 'Self driving is also available along with driving';
        }
    }

    $car_obj = new Car;

    // Fails
    //echo $car_obj->engine;

    // public prop
    echo 'Color : ' . $car_obj->color;
    echo 'Price : ' . $car_obj->price;

?>