Access modifiers (public, private, protected) in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code with access modifiers?

Consider this PHP class and code snippet. What will be printed?

PHP

<?php
class Test {
    public $a = 1;
    private $b = 2;
    protected $c = 3;

    public function printValues() {
        echo $this->a . ',' . $this->b . ',' . $this->c;
    }
}

$test = new Test();
echo $test->a . ',';
// echo $test->b . ','; // Uncommenting this line causes error
// echo $test->c; // Uncommenting this line causes error
$test->printValues();
?>

A 1,1,2,3

B 1,2,3

C 1,1,2

D 1,1,3

💡 Hint

Remember that private and protected properties cannot be accessed directly outside the class, but public properties can.

The public property $a is accessible directly and prints '1,'. The private $b and protected $c cannot be accessed directly outside the class, so those lines are commented out. The printValues() method inside the class can access all three properties and prints '1,2,3'. So the full output is '1,1,2,3'.

❓ Predict Output

intermediate

What error occurs when accessing a private property from outside the class?

What error will this PHP code produce?

PHP

<?php
class Sample {
    private $secret = 'hidden';
}

$obj = new Sample();
echo $obj->secret;
?>

A No output, prints 'hidden'

B Parse error: syntax error, unexpected 'private'

C Fatal error: Uncaught Error: Cannot access private property Sample::$secret

D Notice: Undefined property: Sample::$secret

💡 Hint

Private properties cannot be accessed from outside the class.

Trying to access a private property directly from outside the class causes a fatal error in PHP. The error message says you cannot access the private property.

🔧 Debug

advanced

Why does this code cause an error when accessing a protected property?

Look at this PHP code. Why does it cause an error?

PHP

<?php
class ParentClass {
    protected $value = 10;
}

class ChildClass extends ParentClass {
}

$obj = new ChildClass();
echo $obj->value;
?>

A Protected properties cannot be accessed directly outside the class or its children

B Protected properties can only be accessed inside the parent class, not children

C The property <code>$value</code> is not declared public, so it is undefined

D PHP does not support protected properties

💡 Hint

Think about where protected properties can be accessed from.

Protected properties can be accessed inside the class where they are declared and in child classes, but not from outside objects. Accessing $obj->value from outside causes an error.

📝 Syntax

advanced

Which option correctly declares a private property and a public method in PHP?

Choose the correct PHP code snippet that declares a private property $data and a public method getData() that returns it.

A class Example { private $data; public getData() { return $this->data; } }

B class Example { private $data; function getData() { return $data; } }

C class Example { public $data; private function getData() { return $this->data; } }

D class Example { private $data; public function getData() { return $this->data; } }

💡 Hint

Remember to use function keyword and $this-> to access properties inside methods.

Option D correctly declares a private property $data and a public method getData() that returns $this->data. Option D misses public and uses $data without $this->. Option D swaps visibility and method access. Option D misses function keyword.

🚀 Application

expert

How many properties are accessible inside this child class method?

Given these classes, how many properties can the showProperties() method access?

PHP

<?php
class Base {
    public $pub = 1;
    private $priv = 2;
    protected $prot = 3;
}

class Derived extends Base {
    public function showProperties() {
        $vars = get_object_vars($this);
        $count = 0;
        if (isset($vars['pub'])) $count++;
        if (isset($vars['priv'])) $count++;
        if (isset($vars['prot'])) $count++;
        return $count;
    }
}

$obj = new Derived();
echo $obj->showProperties();
?>

A 2

B 3

C 1

D 0

💡 Hint

Think about which properties are accessible inside a child class method.

The child class method can access public and protected properties from the parent class, but not private ones. So it counts $pub and $prot, but not $priv. The count is 2.