Properties and visibility in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a public property named $name.

PHP

<?php
class Person {
    [1] $name;
}
?>

Drag options to blanks, or click blank then click option'

Avar

Bprivate

Cprotected

Dpublic

Attempts:

3 left

💡 Hint

Common Mistakes

Using private or protected which restrict access.

The public keyword makes the property accessible from anywhere.

2fill in blank

medium

Complete the code to make the property $age accessible only within the class and its subclasses.

PHP

<?php
class Person {
    [1] $age;
}
?>

Drag options to blanks, or click blank then click option'

Aprivate

Bprotected

Cpublic

Dvar

Attempts:

3 left

💡 Hint

Common Mistakes

Using private which restricts access only to the class itself.

The protected keyword restricts access to the class itself and its subclasses.

3fill in blank

hard

Fix the error in the code by choosing the correct visibility keyword for the property $salary that should be accessible only inside the class.

PHP

<?php
class Employee {
    [1] $salary;
}
?>

Drag options to blanks, or click blank then click option'

Aprivate

Bprotected

Cvar

Dpublic

Attempts:

3 left

💡 Hint

Common Mistakes

Using public or protected which allow wider access.

The private keyword restricts access to the property only within the class itself.

4fill in blank

hard

Fill both blanks to declare a protected property $data and initialize it with an empty array.

PHP

<?php
class Container {
    [1] $data = [2];
}
?>

Drag options to blanks, or click blank then click option'

Aprotected

B[]

Carray()

Dpublic

Attempts:

3 left

💡 Hint

Common Mistakes

Using public instead of protected.

Using array() instead of [] (both valid but only one is correct here).

The property is declared protected and initialized with an empty array using [].

5fill in blank

hard

Fill all three blanks to declare a private property $count, initialize it to zero, and increment it by one inside a method.

PHP

<?php
class Counter {
    [1] $count = [2];

    public function increment() {
        $this->count [3] 1;
    }
}
?>

Drag options to blanks, or click blank then click option'

Aprivate

B0

C+=

Dpublic

Attempts:

3 left

💡 Hint

Common Mistakes

Using public instead of private.

Using =+ instead of += for increment.

The property is declared private, initialized to 0, and incremented using +=.

Practice

1. Which visibility keyword allows a property to be accessed from anywhere, including outside the class?

easy

A. private

B. public

C. protected

D. static

Solution

1. Step 1: Understand visibility keywords

   Public properties can be accessed from anywhere, protected only within the class and subclasses, private only inside the class.

2. Step 2: Identify which keyword allows outside access

   Only public allows access from outside the class.

3. Final Answer:

   public -> Option B

4. Quick Check:

   public = accessible everywhere [OK]

Hint: Public means accessible everywhere, no restrictions [OK]

Common Mistakes:

• Confusing protected with public
• Thinking private allows outside access
• Mixing static with visibility

2. Which of the following is the correct way to declare a private property named $name in a PHP class?

easy

A. private $name;

B. var $name;

C. public $name;

D. protected $name;

Solution

1. Step 1: Recall PHP property declaration syntax

   Properties are declared with visibility keyword followed by variable name and semicolon.

2. Step 2: Identify private property syntax

   Correct syntax is private $name;. The var keyword is outdated and defaults to public.

3. Final Answer:

   private $name; -> Option A

4. Quick Check:

   private property declaration uses 'private' keyword [OK]

Hint: Use 'private' keyword before $property for private visibility [OK]

Common Mistakes:

• Using 'var' instead of visibility keywords
• Omitting the $ sign
• Using public or protected instead of private

3. What will be the output of this PHP code?

class Car {
  private $color = 'red';
  public function getColor() {
    return $this->color;
  }
}
$car = new Car();
echo $car->getColor();

medium

A. Empty string

B. Error: Cannot access private property

C. null

D. red

Solution

1. Step 1: Understand private property access

   The property $color is private, so it cannot be accessed directly outside the class.

2. Step 2: Check method usage to access private property

   The public method getColor() returns the private property value, so calling it outputs 'red'.

3. Final Answer:

   red -> Option D

4. Quick Check:

   Private property accessed via public method = 'red' [OK]

Hint: Use public methods to access private properties safely [OK]

Common Mistakes:

• Trying to access private property directly
• Expecting an error when using a getter method
• Confusing null with private property value

4. Identify the error in this PHP class code:

class Person {
  protected $age;
  public function setAge($age) {
    $this->age = $age;
  }
}
$person = new Person();
echo $person->age;

medium

A. Method setAge should be private

B. Missing semicolon after property declaration

C. Cannot access protected property directly outside class

D. Class name should be lowercase

Solution

1. Step 1: Understand protected property visibility

   Protected properties cannot be accessed directly from outside the class or its subclasses.

2. Step 2: Analyze code usage of protected property

   The code tries to echo $person->age directly, which causes an error due to protected visibility.

3. Final Answer:

   Cannot access protected property directly outside class -> Option C

4. Quick Check:

   Protected = no direct outside access [OK]

Hint: Protected properties need methods for outside access [OK]

Common Mistakes:

• Trying to access protected property directly
• Confusing protected with public
• Ignoring visibility rules

5. Given this PHP class, what is the best way to safely update the private property $score only if the new score is higher?

class Game {
  private $score = 0;
  public function updateScore(int $newScore) {
    // What code should go here?
  }
  public function getScore() {
    return $this->score;
  }
}

hard

A. if ($newScore > $this->score) { $this->score = $newScore; }

B. $this->score = $newScore;

C. return $newScore > $this->score;

D. if ($newScore < $this->score) { $this->score = $newScore; }

Solution

1. Step 1: Understand the requirement to update only if new score is higher

   The property $score should change only when $newScore is greater than current $score.

2. Step 2: Choose the correct conditional update code

   if ($newScore > $this->score) { $this->score = $newScore; } checks if $newScore is greater, then updates $score. Other options either overwrite unconditionally or do wrong comparison.

3. Final Answer:

   if ($newScore > $this->score) { $this->score = $newScore; } -> Option A

4. Quick Check:

   Update only if newScore > current score [OK]

Hint: Use if condition to update private property safely [OK]

Common Mistakes:

• Updating score without condition
• Using wrong comparison operator
• Returning boolean instead of updating property