Singleton pattern in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare the Singleton class property.

PHP

<?php
class Singleton {
    private static [1];
}

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

A$unique

B$object

C$single

D$instance

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-static property for the instance.

Naming the property something other than $instance.

The Singleton class uses a private static property named $instance to hold the single instance.

2fill in blank

medium

Complete the code to prevent creating multiple instances by making the constructor private.

PHP

<?php
class Singleton {
    private function [1]() {}
}

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

A__clone

B__destruct

C__construct

D__invoke

Attempts:

3 left

💡 Hint

Common Mistakes

Making the constructor public or protected.

Confusing constructor with clone or destructor.

The constructor __construct is made private to prevent creating new instances from outside the class.

3fill in blank

hard

Fix the error in the method that returns the single instance.

PHP

<?php
class Singleton {
    private static $instance;
    private function __construct() {}
    public static function getInstance() {
        if (self::[1] === null) {
            self::$instance = new Singleton();
        }
        return self::$instance;
    }
}

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

A$instance

Binstance

C$Instance

DInstance

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the dollar sign when accessing static property.

Using wrong case for the property name.

The static property must be accessed as self::$instance with the dollar sign.

4fill in blank

hard

Fill both blanks to prevent cloning and unserializing the Singleton instance.

PHP

<?php
class Singleton {
    private function [1]() {}
    public function [2]() {
        throw new \Exception("Cannot clone singleton");
    }
}

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

A__wakeup

B__clone

C__sleep

D__destruct

Attempts:

3 left

💡 Hint

Common Mistakes

Not preventing cloning or unserializing.

Using wrong magic method names.

The __wakeup method is made private to prevent unserializing, and __clone is made public but throws an exception to prevent cloning.

5fill in blank

hard

Fill all three blanks to complete the Singleton class with instance property, constructor, and getInstance method.

PHP

<?php
class Singleton {
    private static [1];
    private function [2]() {}
    public static function [3]() {
        if (self::$instance === null) {
            self::$instance = new Singleton();
        }
        return self::$instance;
    }
}

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

A$instance

B__construct

CgetInstance

D__clone

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong names for property or methods.

Making constructor public.

The Singleton class has a private static property $instance, a private constructor __construct, and a public static method getInstance to return the single instance.