Properties and visibility in PHP - Step-by-Step Execution

Concept Flow - Properties and visibility

Define Class with Properties

↓

Set Property Visibility: public/private/protected

↓

Create Object Instance

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Access Properties

This flow shows how properties are defined with visibility and how they can be accessed depending on their visibility.

Execution Sample

PHP

<?php
class Car {
  public $color = 'red';
  private $speed = 0;
}
$car = new Car();
echo $car->color;
echo $car->speed; // error
?>

Defines a class with public and private properties, then accesses the public property successfully and shows private property access causes error.

Execution Table

Step	Action	Property Access	Result	Notes
1	Create object $car	N/A	Object created	Properties initialized: color='red', speed=0
2	Access $car->color	public	Outputs 'red'	Public property accessible from outside
3	Access $car->speed	private	Error: Cannot access private property	Private property not accessible outside class
4	End	N/A	Execution stops due to error	Private property access blocked

💡 Execution stops at step 3 because private property access from outside the class is not allowed.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3
$car->color	undefined	'red'	'red'	'red'
$car->speed	undefined	0	0	0

Key Moments - 2 Insights

Why does accessing $car->speed cause an error?

Because $speed is declared private, it cannot be accessed from outside the class. See execution_table step 3.

Can we access $car->color from outside the class?

Yes, because $color is declared public, it is accessible from outside. See execution_table step 2.

Visual Quiz - 3 Questions

Look at the execution table, what is the output when accessing $car->color at step 2?

A 'red'

B Error

C null

D Undefined property

💡 Hint

Check execution_table row with Step 2 for the output of $car->color access.

At which step does the program stop due to an error?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

See execution_table exit_note and step 3 where private property access causes error.

If $speed was declared public instead of private, what would happen at step 3?

A Output 'red'

B Error

C Output '0'

D No change

💡 Hint

Refer to variable_tracker and execution_table step 3 about property visibility effects.

Concept Snapshot

Properties in PHP classes have visibility: public, private, or protected.
Public properties can be accessed anywhere.
Private properties can only be accessed inside the class.
Protected properties can be accessed inside the class and subclasses.
Trying to access private or protected properties from outside causes errors.

Full Transcript

This example shows a PHP class Car with two properties: color (public) and speed (private). When we create an object of Car, the properties are initialized. Accessing the public property color from outside the class works and outputs 'red'. However, trying to access the private property speed from outside causes an error and stops execution. This demonstrates how property visibility controls access in PHP classes.