What is the difference between public, private, and protected in PHP?

Question

When and why should I use `public`, `private`, and `protected` functions and variables inside a class? What is the difference between them? Examples: // Public public $variable; public function doSomething() { // ... } // Private private $variable; private function doSomething() { // ... } // Protected protected $variable; protected function doSomething() { // ... }

Answer 1

The concepts of public, private, and protected carry across all OOP languages, including PHP.

The idea is that the data inside a class should be hidden and not accessible from outside the class unless it absolutely has to be. So, these keywords do just that.

public - This is for data and methods that should be accessible outside the class. Think of this as your "public API" -- the functions that your class exposes so that people can use your class / library.

private - This is for "internal" data and functions. Things that no one needs to know about. Anything labeled private is inaccessible outside of the class. Attempting to access a private variable or method will result in an error.

protected - This is like "private", in that the data is inaccessible outside of the class -- *except* for subclasses. Any subclass that extends the class has access to these "protected" data and functions.

For example, if I have a class Dad:

class Dad

{

private $bank_account;

protected $moms_phone_number = '555-3318'

public function buySomething($cost)

{

$bank_account->deduct($cost);

}

}

A dad can `buySomething` but we don't want to give access to the underlying bank_account object -- we only need to allow access to the buySomething method to instances of Dad. Here, $john buys something that costs $1.00:

$john = new Dad();

$john->buySomething(1.00);

A child class, Son, may need access to $moms_phone_number in order to give her a call, so we make that variable protected in Dad class so that the Son, $jimmy, has access to it:

class Son Extends Dad

{

private $smartphone

public function callMom()

{

$smartphone->call($this->moms_phone_number)

}

}

$jimmy = new Son();

$jimmy->callMom();

I hope this helps.

The official documentation on this: https://www.php.net/manual/en/language.oop5.visibility.php