Singleton pattern in PHP - Mini Project: Build & Apply

Singleton pattern

📖 Scenario: You are building a PHP application where you need to ensure that only one instance of a class is created. This is useful when managing a single connection or configuration throughout your app.

🎯 Goal: Create a Singleton class in PHP that allows only one instance to be created and provides a method to get that instance.

📋 What You'll Learn

Create a class called Singleton

Add a private static variable called $instance to hold the single instance

Add a private constructor to prevent creating new instances from outside

Add a public static method called getInstance() that returns the single instance

Add a public method called showMessage() that prints a message to confirm the instance

💡 Why This Matters

🌍 Real World

Singleton pattern is used to manage shared resources like database connections or configuration settings where only one instance should exist.

💼 Career

Understanding Singleton helps in designing efficient and safe applications, a common requirement in backend and system programming jobs.

1

Create the Singleton class with a private static variable

Create a class called Singleton with a private static variable called $instance initialized to null.

PHP

<?php

// Your code here

Need a hint?

Use private static ?Singleton $instance = null; inside the class.

2

Add a private constructor to prevent outside instantiation

Inside the Singleton class, add a private constructor method __construct() with an empty body.

PHP

<?php

class Singleton {
    private static ?Singleton $instance = null;

    // Your code here
}

Need a hint?

Define private function __construct() { } inside the class.

3

Add the public static getInstance() method

Inside the Singleton class, add a public static method called getInstance() that checks if self::$instance is null. If it is, create a new Singleton and assign it to self::$instance. Then return self::$instance.

PHP

<?php

class Singleton {
    private static ?Singleton $instance = null;

    private function __construct() {
        // private constructor to prevent direct creation
    }

    // Your code here
}

Need a hint?

Use public static function getInstance() with a check for self::$instance === null.

4

Add a method to show a message and print the singleton instance message

Inside the Singleton class, add a public method called showMessage() that prints "This is the Singleton instance.". Then, outside the class, get the singleton instance by calling Singleton::getInstance() and call showMessage() on it.

PHP

<?php

class Singleton {
    private static ?Singleton $instance = null;

    private function __construct() {
        // private constructor to prevent direct creation
    }

    public static function getInstance(): Singleton {
        if (self::$instance === null) {
            self::$instance = new Singleton();
        }
        return self::$instance;
    }

    // Your code here
}

// Your code here

Need a hint?

Define public function showMessage() that echoes the message. Then call it on the instance returned by Singleton::getInstance().