PHP
private access
Learn that private access is limited to the defining class only.
The private access modifier
private is the strictest visibility. When a property or method is private, it can only be accessed inside the class that declares it. Even subclasses cannot reach it.
For example, class Counter { private int $count = 0; } means $count is only reachable from Counter's own methods via $this->count. Trying to access it from outside or from a subclass triggers a fatal error.
private is used when you want to fully hide a class's internal implementation. It is the cornerstone of encapsulation and prevents outside code from breaking internal state.
private cannot be reached from subclasses
Consider this example: start with class Account { private float $balance = 0; }. If you then declare class Savings extends Account { public function peek() { return $this->balance; } }, calling Savings->peek() triggers a fatal error.
Because $balance is private, Savings cannot access it even though it extends Account. This is the core difference between protected and private: protected is open to subclasses, private is only to the declaring class.
If a subclass needs this data, the parent must expose a public or protected method, or change the property to protected.
Exercise Counter class with a private property
Define a Counter class with a private int $count = 0 property. Add a public function increment(): void method that does $this->count++. Also add public function getCount(): int that does return $this->count. Then create $counter = new Counter(), call $counter->increment() three times and print echo $counter->getCount() . "\n".
Show example solution
Declare private $count, increment does $this->count++, getCount returns $this->count.
Example solution:
<?php
// Define a Counter class with a private property
class Counter {
private int $count = 0;
public function increment(): void {
$this->count++;
}
public function getCount(): int {
return $this->count;
}
}
$counter = new Counter();
$counter->increment();
$counter->increment();
$counter->increment();
echo $counter->getCount() . "\n";
Test yourself
-
Declare a private property
class Counter {
____
}
Show answer
class Counter {
private $count;
}
-
What happens if a subclass tries to reach a private property?
- It can, because subclasses inherit
- Only if it is also marked protected
- Fatal error: Cannot access private property
- It warns but still reaches it
Show answer
Fatal error: Cannot access private property — Correct. private members cannot be reached even from subclasses; PHP throws a fatal error.
-
Match the visibility modes
- private $count
- Declaring class only
- public $count
- Accessible everywhere
- protected $count
- Class and subclasses
- var $count
- Legacy, public
Next lesson: Encapsulation
