Instanceof operator in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if $obj is an instance of the class MyClass.

PHP

<?php
class MyClass {}
$obj = new MyClass();
if ($obj [1] MyClass) {
    echo "Yes";
} else {
    echo "No";
}
?>

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

A===

B==

Cinstanceof

Dis_a

Attempts:

3 left

💡 Hint

Common Mistakes

Using == or === instead of instanceof.

Using is_a as if it were an operator.

The instanceof operator checks if an object is an instance of a specific class.

2fill in blank

medium

Complete the code to check if $animal is an instance of the class Dog.

PHP

<?php
class Dog {}
class Cat {}
$animal = new Dog();
if ($animal [1] Dog) {
    echo "It's a dog.";
} else {
    echo "It's not a dog.";
}
?>

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

A==

Binstanceof

Cis_a

D===

Attempts:

3 left

💡 Hint

Common Mistakes

Using == or === which compare values, not types.

Trying to use is_a as an operator.

instanceof checks if $animal is an instance of Dog or its subclass.

3fill in blank

hard

Fix the error in the code to correctly check if $obj is an instance of MyInterface.

PHP

<?php
interface MyInterface {}
class MyClass implements MyInterface {}
$obj = new MyClass();
if ($obj [1] MyInterface) {
    echo "Implements interface.";
} else {
    echo "Does not implement interface.";
}
?>

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

A===

B==

Cis_a

Dinstanceof

Attempts:

3 left

💡 Hint

Common Mistakes

Using == or === which do not check interface implementation.

Trying to use is_a as an operator.

instanceof works with interfaces to check if an object implements them.

4fill in blank

hard

Fill in the blank to create a dictionary with words as keys and their lengths as values, but only for words longer than 3 characters.

PHP

<?php
$words = ['apple', 'cat', 'banana', 'dog'];
$lengths = array_filter(array_combine($words, array_map(function($word) {
    return strlen($word);
}, $words)), function($length) {
    return $length [1] 3;
});
print_r($lengths);
?>

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

A>

B<

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using < or == which filter wrong lengths.

Using != which includes unwanted lengths.

We want lengths greater than 3, so use > operator.

5fill in blank

hard

Fill all three blanks to create an associative array with uppercase words as keys and their lengths as values, only for words longer than 3 characters.

PHP

<?php
$words = ['apple', 'cat', 'banana', 'dog'];
$lengths = array_filter(array_combine(array_map(function($word) {
    return [1];
}, $words), array_map(function($word) {
    return [2];
}, $words)), function($length) {
    return $length [3] 3;
});
print_r($lengths);
?>

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

A$word strtoupper($word)

Bstrlen($word)

C>

Dstrtoupper($word)

Attempts:

3 left

💡 Hint

Common Mistakes

Using $word instead of strtoupper($word) for keys.

Using wrong comparison operator in filter.

Mixing keys and values in array_combine.

Use strtoupper($word) for keys, strlen($word) for values, and > 3 to filter lengths.

Practice

1. What does the instanceof operator do in PHP?

easy

A. Creates a new instance of a class

B. Checks if an object is an instance of a specific class or its subclass

C. Deletes an object from memory

D. Converts an object to a string

Solution

1. Step 1: Understand the purpose of instanceof

   The instanceof operator is used to check if a variable is an object of a certain class or subclass.

2. Step 2: Differentiate from other operations

   It does not create, delete, or convert objects; it only checks their type.

3. Final Answer:

   Checks if an object is an instance of a specific class or its subclass -> Option B

4. Quick Check:

   instanceof checks object type [OK]

Hint: Remember: instanceof checks object type, not creation or deletion [OK]

Common Mistakes:

• Confusing instanceof with object creation
• Thinking instanceof deletes objects
• Assuming instanceof converts objects to strings

2. Which of the following is the correct syntax to check if $obj is an instance of class Car?

easy

A. if ($obj instance Car) {}

B. if ($obj is Car) {}

C. if (instanceof $obj Car) {}

D. if ($obj instanceof Car) {}

Solution

1. Step 1: Recall correct instanceof syntax

   The correct syntax is: variable instanceof ClassName, without extra keywords or rearrangement.

2. Step 2: Check each option

   if ($obj instanceof Car) {} matches the correct syntax exactly. Others have wrong keywords or order.

3. Final Answer:

   if ($obj instanceof Car) {} -> Option D

4. Quick Check:

   Correct instanceof syntax [OK]

Hint: Syntax is always: variable instanceof ClassName [OK]

Common Mistakes:

• Using 'is' instead of 'instanceof'
• Reversing order of variable and class
• Adding extra keywords inside condition

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

$a = new DateTime();
if ($a instanceof DateTime) {
    echo 'Yes';
} else {
    echo 'No';
}

medium

A. Yes

B. No

C. Error

D. Nothing

Solution

1. Step 1: Understand object creation

   $a is created as a new instance of the DateTime class.

2. Step 2: Check instanceof condition

   The condition $a instanceof DateTime is true because $a is exactly a DateTime object.

3. Final Answer:

   Yes -> Option A

4. Quick Check:

   Object is DateTime = Yes [OK]

Hint: If object matches class, instanceof returns true [OK]

Common Mistakes:

• Assuming instanceof returns false for exact class
• Expecting syntax error from instanceof
• Ignoring else branch output

4. Identify the error in this PHP code snippet:

class Animal {}
class Dog extends Animal {}
$dog = new Dog();
if ($dog instanceof 'Animal') {
    echo 'It is an animal';
}

medium

A. Missing semicolon after class definition

B. Incorrect object creation syntax

C. Using quotes around class name in instanceof

D. Using instanceof with a variable instead of object

Solution

1. Step 1: Check instanceof usage

   The instanceof operator expects a class name without quotes, not a string.

2. Step 2: Verify other parts

   Classes and object creation are correct; semicolons are present.

3. Final Answer:

   Using quotes around class name in instanceof -> Option C

4. Quick Check:

   Class name must be unquoted in instanceof [OK]

Hint: Do not put quotes around class names in instanceof [OK]

Common Mistakes:

• Putting class names in quotes inside instanceof
• Confusing instanceof with string comparison
• Missing semicolons elsewhere (not in this code)

5. Given the classes below, what will be the output?

class Vehicle {}
class Car extends Vehicle {}
class Bike extends Vehicle {}

function checkVehicle($obj) {
    if ($obj instanceof Car) {
        return 'Car';
    } elseif ($obj instanceof Vehicle) {
        return 'Vehicle';
    } else {
        return 'Unknown';
    }
}

$myBike = new Bike();
echo checkVehicle($myBike);

hard

A. Vehicle

B. Unknown

C. Car

D. Error

Solution

1. Step 1: Analyze object type

   $myBike is an instance of Bike, which extends Vehicle.

2. Step 2: Follow function logic

   First condition checks if $obj is Car - false. Second checks if $obj is Vehicle - true because Bike is subclass of Vehicle.

3. Final Answer:

   Vehicle -> Option A

4. Quick Check:

   Bike is a Vehicle, not Car = Vehicle [OK]

Hint: Check subclass before superclass in instanceof chains [OK]

Common Mistakes:

• Expecting 'Car' for Bike object
• Ignoring subclass relationship in instanceof
• Assuming instanceof only matches exact class