Object instantiation with new in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new instance of the class.

PHP

<?php
class Car {}
$myCar = [1] Car();
?>

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

Anew

Bcreate

Cmake

Dbuild

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'create' or 'make' instead of 'new' to instantiate an object.

In PHP, you create a new object by using the new keyword followed by the class name and parentheses.

2fill in blank

medium

Complete the code to instantiate the class and assign it to a variable.

PHP

<?php
class Dog {}
$dog = [1] Dog();
echo get_class($dog);
?>

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

Amake

Bcreate

Cnew

Dbuild

Attempts:

3 left

💡 Hint

Common Mistakes

Using other verbs like 'make' or 'create' which are not valid in PHP for object instantiation.

The new keyword is used to create an instance of the Dog class.

3fill in blank

hard

Fix the error in the code to correctly instantiate the class.

PHP

<?php
class Book {}
$book = [1] Book();
?>

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

A()

B->

C[]

Dnew

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to call the class name as a function without 'new'.

You must use the new keyword before the class name to create an object.

4fill in blank

hard

Complete the code to instantiate the class and call its method.

PHP

<?php
class Person {
    function greet() {
        return "Hello!";
    }
}
$person = [1] Person();
echo $person->greet();
?>

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

Anew

B->

C::

D.

Attempts:

3 left

💡 Hint

Common Mistakes

Using '::' instead of '->' to call an instance method.

Use new to create the object and -> to call its method.

5fill in blank

hard

Fill both blanks to instantiate the class with a constructor and access its property.

PHP

<?php
class Animal {
    public $name;
    function __construct($name) {
        $this->name = $name;
    }
}
$animal = [1] Animal([2]);
echo $animal->name;
?>

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

Anew

B"Lion"

C->

D'Tiger'

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to use quotes around the string argument.

Using '.' instead of '->' to access the property.

Use new to create the object, pass the name as a string, and use -> to access the property.

Practice

1.

What does the new keyword do in PHP?

easy

A. It deletes an existing object.

B. It defines a new class.

C. It calls a function inside a class.

D. It creates a new instance of a class (an object).

Solution

1. Step 1: Understand the role of new

   The new keyword is used to create an object from a class blueprint.

2. Step 2: Differentiate from other keywords

   It does not delete objects, call functions, or define classes; it only creates objects.

3. Final Answer:

   It creates a new instance of a class (an object). -> Option D

4. Quick Check:

   new creates objects [OK]

Hint: Remember: new = create object from class [OK]

Common Mistakes:

• Thinking new deletes objects
• Confusing new with function calls
• Believing new defines classes

2.

Which of the following is the correct syntax to create a new object of class Car?

class Car {
  // class body
}

// Create object here

easy

A. $car = new Car();

B. $car = Car();

C. new $car = Car();

D. $car = Car.new();

Solution

1. Step 1: Recall PHP object creation syntax

   In PHP, to create an object, use $variable = new ClassName();.

2. Step 2: Check each option

   $car = new Car(); matches the correct syntax. The other options use invalid syntax: new before variable assignment, omitting the new keyword, or using dot notation.

3. Final Answer:

   $car = new Car(); -> Option A

4. Quick Check:

   Use new ClassName() to create objects [OK]

Hint: Use $obj = new ClassName(); always [OK]

Common Mistakes:

• Omitting the new keyword
• Placing new after variable
• Using dot notation like other languages

3.

What will be the output of the following PHP code?

class Dog {
  public $name;
  public function __construct($name) {
    $this->name = $name;
  }
  public function bark() {
    return "Woof! I am " . $this->name;
  }
}

$dog = new Dog("Buddy");
echo $dog->bark();

medium

A. Woof! I am Buddy

B. Woof! I am $name

C. Error: Undefined property

D. Woof! I am

Solution

1. Step 1: Understand constructor usage

   The constructor sets the name property to "Buddy" when the object is created.

2. Step 2: Analyze the bark method output

   The bark() method returns "Woof! I am " concatenated with the name property, which is "Buddy".

3. Final Answer:

   Woof! I am Buddy -> Option A

4. Quick Check:

   Constructor sets name, bark returns it [OK]

Hint: Constructor sets data; methods use it [OK]

Common Mistakes:

• Ignoring constructor parameters
• Using variable name instead of property
• Expecting syntax error due to missing parentheses

4.

Identify the error in this PHP code snippet:

class Person {
  public $age;
  public function __construct($age) {
    $this->age = $age;
  }
}

$person = Person(25);
echo $person->age;

medium

A. Property age should be private.

B. Constructor should not have parameters.

C. Missing new keyword when creating the object.

D. Cannot echo object property directly.

Solution

1. Step 1: Check object instantiation syntax

   The object is created by calling Person(25) without new, which is invalid in PHP.

2. Step 2: Correct the instantiation

   Use $person = new Person(25); to create the object properly.

3. Final Answer:

   Missing new keyword when creating the object. -> Option C

4. Quick Check:

   Always use new to instantiate objects [OK]

Hint: Always use new before class name to create object [OK]

Common Mistakes:

• Forgetting new keyword
• Thinking constructor can't have parameters
• Confusing property visibility with errors

5.

Given this class:

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

// Create an array of books with titles and authors
$booksData = [
  ['1984', 'George Orwell'],
  ['Brave New World', 'Aldous Huxley'],
  ['Fahrenheit 451', 'Ray Bradbury']
];

// Fill this array with Book objects
$books = [];
foreach ($booksData as $data) {
  // Fill here
}

Which line correctly creates and adds a new Book object to $books inside the loop?

hard

A. $books[] = new Book($data[1], $data[0]);

B. $books[] = new Book($data[0], $data[1]);

C. $books[] = new Book($data);

D. $books[] = Book($data[0], $data[1]);

Solution

1. Step 1: Understand constructor parameters

   The constructor expects two parameters: title and author, in that order.

2. Step 2: Match data array to constructor

   $data[0] is title, $data[1] is author, so new Book($data[0], $data[1]) is correct.

3. Step 3: Add object to array

   Using $books[] = appends the new object to the array.

4. Final Answer:

   $books[] = new Book($data[0], $data[1]); -> Option B

5. Quick Check:

   Use new with correct params and append [OK]

Hint: Match constructor params order exactly when using new [OK]

Common Mistakes:

• Omitting new keyword
• Passing whole array instead of separate params
• Swapping title and author order