Summary - Visibility

PHP course · Intermediate · Lesson 29/115

Build a temperature class with public, private, getter and setter.

Summary - Visibility

In this group you learned three visibility modes:

public: accessible everywhere.
protected: class and subclasses.
private: only the declaring class.

For encapsulation, make internal state private and expose controlled access with getters and setters. Validation in setters protects invariants. Now you'll combine all of this in a Temperature class.

Exercise Temperature class: encapsulation combined

Define a Temperature class with a private float $celsius = 0 property. Add public function setCelsius(float $value): void that rejects below absolute zero with if ($value < -273) { return; } and then runs $this->celsius = $value. Add public function getCelsius(): float that does return $this->celsius. Then create $temp = new Temperature(), call $temp->setCelsius(-500) (rejected), then $temp->setCelsius(25), and print echo $temp->getCelsius() . "\n".

Show example solution

Declare private float $celsius. In setCelsius add if ($value < -273) return; then $this->celsius = $value. getCelsius returns $this->celsius.
Example solution:
<?php
// Define a Temperature class
class Temperature {
    private float $celsius = 0;
    public function setCelsius(float $value): void {
        if ($value < -273) {
            return;
        }
        $this->celsius = $value;
    }
    public function getCelsius(): float {
        return $this->celsius;
    }
}
$temp = new Temperature();
$temp->setCelsius(-500);
$temp->setCelsius(25);
echo $temp->getCelsius() . "\n";

Tips for choosing visibility

Remember: public for broad access, protected for inheritance hierarchy, private for class-only. Which to choose depends on who needs to see the data.

Internal state starts private; open to protected only when needed. Expose behavior, not data. This makes code easier to change: you can alter the internal representation without breaking outside callers.

In the next group we'll look at static members for class-level data.

Test yourself

Match all visibility modes

public

Accessible everywhere
protected

Class and subclasses
private

Class only
Setter + Getter

Controlled access
Which visibility fits a bank account balance?
- public - changeable everywhere
- private - class only, with a setter
- protected - subclasses can change it
- No visibility needed
Show answer

private - class only, with a setter — Correct. Balance should be private and change only via deposit/withdraw methods.

Summary - Visibility