Constructor method in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP constructor example?

Consider the following PHP class with a constructor. What will be printed when the code runs?

PHP

<?php
class Car {
    public $model;
    public function __construct($model) {
        $this->model = $model;
        echo "Car model is: " . $this->model . "\n";
    }
}
$car = new Car("Toyota");
?>

A No output

B Car model is:

C Fatal error: Constructor method not found

D Car model is: Toyota

💡 Hint

Look at what the constructor does when the object is created.

The constructor __construct is called automatically when a new object is created. It prints the model name passed during object creation.

❓ Predict Output

intermediate

What will be the value of $obj->name after this code runs?

Look at this PHP class with a constructor. What is the value of the property name after creating the object?

PHP

<?php
class Person {
    public $name;
    public function __construct($name) {
        $this->name = $name;
    }
}
$obj = new Person("Alice");
// What is $obj->name?
?>

A "Alice"

B "name"

C Undefined property error

D null

💡 Hint

The constructor sets the property from the argument.

The constructor assigns the passed argument "Alice" to the property name. So $obj->name is "Alice".

🔧 Debug

advanced

What error does this PHP constructor code produce?

This PHP class tries to use a constructor but has a mistake. What error will it cause?

PHP

<?php
class Animal {
    public $type;
    public function Animal($type) {
        $this->type = $type;
    }
}
$dog = new Animal("Dog");
echo $dog->type;
?>

A Outputs: Dog

B Notice: Undefined property: Animal::$type

C Fatal error: Call to undefined method Animal::__construct()

D Parse error: syntax error

💡 Hint

PHP 7+ uses __construct() as the constructor method, not the class name.

In modern PHP versions, the constructor must be named __construct(). Naming it the same as the class does not work and __construct() is missing, causing a fatal error.

🧠 Conceptual

advanced

Which statement about PHP constructors is true?

Choose the correct statement about constructor methods in PHP classes.

A Constructors cannot accept parameters in PHP.

B The constructor method __construct() is called automatically when an object is created.

C The constructor method must always be named after the class name.

D You must call the constructor manually after creating an object.

💡 Hint

Think about what happens when you create a new object.

In PHP, the __construct() method is called automatically when a new object is created. It can accept parameters and is the standard constructor method.

📝 Syntax

expert

Which option correctly defines a PHP constructor with a default parameter?

Select the PHP constructor method that correctly sets a default value for a parameter.

A public function __construct($name ?: "Guest") { $this->name = $name; }

B public function __construct($name) = "Guest" { $this->name = $name; }

C public function __construct($name = "Guest") { $this->name = $name; }

D public function __construct($name = Guest) { $this->name = $name; }

💡 Hint

Default parameters use = with quotes for strings.

Option C correctly uses = "Guest" to set a default string parameter. Option C and C have invalid syntax. Option C misses quotes around Guest.