Constructor method in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a constructor method in the class.

PHP

<?php
class Car {
    public function [1]() {
        echo "Car created!";
    }
}
$car = new Car();
?>

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

Acreate

Bconstructor

C__construct

Dinit

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'constructor' instead of '__construct'.

Forgetting the double underscores.

In PHP, the constructor method is named __construct. It runs automatically when an object is created.

2fill in blank

medium

Complete the constructor to accept a parameter and assign it to a property.

PHP

<?php
class Car {
    public $color;
    public function __construct([1]) {
        $this->color = $color;
    }
}
$car = new Car('red');
echo $car->color;

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

A$color

Bcolor

C$this->color

Dthis->color

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the dollar sign in the parameter.

Using property syntax in the parameter list.

The constructor parameter must be a variable with a dollar sign, like $color, to receive the value.

3fill in blank

hard

Fix the error in the constructor method name.

PHP

<?php
class Bike {
    public function [1]() {
        echo "Bike ready!";
    }
}
$bike = new Bike();
?>

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

Aconstruct

B__construct

C_construct

Dconstructor

Attempts:

3 left

💡 Hint

Common Mistakes

Using only one underscore.

Using 'constructor' instead of '__construct'.

The correct constructor method name in PHP is __construct with two underscores at the start.

4fill in blank

hard

Fill both blanks to create a constructor that sets two properties.

PHP

<?php
class Person {
    public $name;
    public $age;
    public function __construct([1], [2]) {
        $this->name = $name;
        $this->age = $age;
    }
}
$person = new Person('Alice', 30);
echo $person->name . ' is ' . $person->age . ' years old.';

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

A$name

B$age

Cname

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Using property names without dollar signs as parameters.

Mixing variable and property names.

The constructor parameters must be variables with dollar signs: $name and $age.

5fill in blank

hard

Fill all three blanks to create a constructor that sets a property and calls a method.

PHP

<?php
class Dog {
    public $breed;
    public function __construct([1]) {
        $this->breed = $breed;
        $this->[2]();
    }
    private function [3]() {
        echo "Dog breed is set.";
    }
}
$dog = new Dog('Beagle');

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

A$breed

Bbark

CshowMessage

Ddisplay

Attempts:

3 left

💡 Hint

Common Mistakes

Calling a method that is not defined.

Using method names that don't match.

The constructor parameter is $breed. The method called is display, so both blanks use 'display'.

Practice

1. What is the main purpose of a constructor method in a PHP class?

easy

A. To print the object details

B. To delete an object from memory

C. To automatically set up an object when it is created

D. To create a new class inside the existing class

Solution

1. Step 1: Understand what a constructor does

   A constructor is a special method that runs automatically when an object is created.

2. Step 2: Identify the purpose of this automatic setup

   This setup usually initializes properties or runs code needed for the object to work properly.

3. Final Answer:

   To automatically set up an object when it is created -> Option C

4. Quick Check:

   Constructor = automatic setup [OK]

Hint: Constructor runs automatically on object creation [OK]

Common Mistakes:

• Thinking constructor deletes objects
• Confusing constructor with printing methods
• Assuming constructor creates new classes

2. Which of the following is the correct way to declare a constructor method in PHP?

easy

A. function __construct() {}

B. function construct() {}

C. function _construct() {}

D. function __destruct() {}

Solution

1. Step 1: Recall the special constructor name in PHP

   PHP uses the exact name __construct with two underscores at the start.

2. Step 2: Check each option for correct syntax

   Only function __construct() {} uses the correct spelling and underscores for the constructor.

3. Final Answer:

   function __construct() {} -> Option A

4. Quick Check:

   Constructor name = __construct [OK]

Hint: Constructor always named __construct with two underscores [OK]

Common Mistakes:

• Missing one or both underscores
• Using 'construct' without underscores
• Confusing constructor with destructor (__destruct)

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

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

medium

A. red

B. Car

C. null

D. Error

Solution

1. Step 1: Understand constructor parameter usage

   The constructor sets the property color to the value passed ('red').

2. Step 2: Check what getColor() returns

   getColor() returns the color property, which was set to 'red'.

3. Final Answer:

   red -> Option A

4. Quick Check:

   Constructor sets color = 'red' [OK]

Hint: Constructor sets properties used later [OK]

Common Mistakes:

• Forgetting to pass argument to constructor
• Expecting class name as output
• Assuming property is null without initialization

4. Identify the error in this PHP class constructor code:

class Person {
  public $name;
  public function __construct {
    $this->name = 'Alice';
  }
}

medium

A. Constructor name should be Person

B. Wrong property name

C. Missing semicolon after assignment

D. Missing parentheses after __construct

Solution

1. Step 1: Check constructor syntax

   In PHP, the constructor method must have parentheses even if no parameters are used.

2. Step 2: Identify the missing parentheses

   The code misses () after __construct, causing a syntax error.

3. Final Answer:

   Missing parentheses after __construct -> Option D

4. Quick Check:

   Constructor needs () even if empty [OK]

Hint: Always add () after __construct even if empty [OK]

Common Mistakes:

• Omitting parentheses in method declaration
• Thinking constructor name must match class
• Forgetting semicolon after statements

5. You want to create a PHP class Book that stores a title and author. The constructor should accept both values and store them. Which code correctly implements this?

hard

A. class Book {
public $title, $author;
public function Book($title, $author) {
$this->title = $title;
$this->author = $author;
}
}

B. class Book {
public $title;
public $author;
public function __construct($title, $author) {
$this->title = $title;
$this->author = $author;
}
}

C. class Book {
public $title;
public $author;
public function __construct() {
$title = '';
$author = '';
}
}

D. class Book {
public $title;
public $author;
public function __construct($title) {
$this->title = $title;
}
}

Solution

1. Step 1: Check constructor name and parameters

   PHP uses __construct with two parameters $title and $author, matching the requirement.

2. Step 2: Verify property assignments

   The code assigns both $title and $author to object properties using $this correctly.

3. Final Answer:

   class Book { public $title; public $author; public function __construct($title, $author) { $this->title = $title; $this->author = $author; } } -> Option B

4. Quick Check:

   Constructor with all needed parameters and assignments [OK]

Hint: Use __construct with all needed parameters and assign to properties [OK]

Common Mistakes:

• Using old-style constructor named after class
• Not passing all required parameters
• Not assigning parameters to properties