Object instantiation with new in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code?

Consider this PHP code that creates a new object and accesses its property. What will it print?

PHP

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

A Buddy

B Dog

C Error: Undefined property

D NULL

💡 Hint

Look at how the constructor sets the property and what is echoed.

The constructor sets the name property to 'Buddy'. Accessing $dog->name prints 'Buddy'.

❓ Predict Output

intermediate

What will this PHP code output?

This code creates two objects from the same class. What will be printed?

PHP

<?php
class Counter {
    public static $count = 0;
    public function __construct() {
        self::$count++;
    }
}
$a = new Counter();
$b = new Counter();
echo Counter::$count;
?>

A Error: Cannot access static property

B 1

C 0

D 2

💡 Hint

Static properties are shared across all instances.

Each time a Counter object is created, the static property $count increments. Two objects means $count is 2.

🔧 Debug

advanced

What error does this PHP code produce?

This code tries to create an object but has a mistake. What error will it cause?

PHP

<?php
class Car {
    private $model;
    public function __construct($model) {
        $this->model = $model;
    }
}
$car = new Car();
echo $car->model;
?>

A Fatal error: Cannot access private property Car::$model

B Notice: Undefined property: model

C Fatal error: Missing argument 1 for Car::__construct()

D No error, outputs empty string

💡 Hint

Check the constructor parameters and how the object is created.

The constructor requires one argument, but none was given, causing a fatal error.

📝 Syntax

advanced

Which option will cause a syntax error in PHP?

Look at these ways to instantiate an object. Which one is NOT valid PHP syntax?

A $obj = new MyClass();

B $obj = new MyClass[];

C $obj = new MyClass;

D $obj = new MyClass(5);

💡 Hint

Check the use of brackets after the class name.

Using square brackets [] after the class name is invalid syntax for object instantiation.

🚀 Application

expert

How many objects are created and what is the output?

This code creates objects inside a loop and prints a property. How many objects are created and what is printed?

PHP

<?php
class Item {
    public $id;
    public function __construct($id) {
        $this->id = $id;
    }
}
$items = [];
for ($i = 1; $i <= 3; $i++) {
    $items[] = new Item($i);
}
foreach ($items as $item) {
    echo $item->id . " ";
}
?>

A 3 objects created; output: '1 2 3 '

B 1 object created; output: '3 '

C 3 objects created; output: '3 3 3 '

D Error: Cannot use object in array

💡 Hint

Each loop iteration creates a new object with a different id.

The loop runs 3 times, creating 3 objects with ids 1, 2, and 3. The foreach prints each id separated by space.