PHP Class: Singleton design pattern implementation

PHP OOP: Exercise-18 with Solution

Write a PHP class called 'Logger' that uses the singleton design pattern to ensure only one instance of the class can be created.

Sample Solution:

PHP Code :

class Logger {
    private static $instance;
    private $logs;

    private function __construct() {
        $this->logs = [];

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

        return self::$instance;

    public function log($message) {
        $this->logs[] = $message;

    public function getLogs() {
        return $this->logs;

$logger = Logger::getInstance();
$logger->log("Log message 1</br>");
$logger->log("Log message 2</br>");

$logs = $logger->getLogs();
foreach ($logs as $log) {
    echo $log . "\n";


Sample Output:

Log message 1
Log message 2


In the above exercise -

  • The "Logger" class has a private static property $instance to hold the singleton instance of the class.
  • The constructor method __construct() is made private to prevent direct class instantiation.
  • The static method getInstance() is implemented as a static factory method. It checks if an instance of the Logger class already exists. If not, it creates a new instance. This method ensures that only one instance of the class can be created.
  • The log($message) method logs a message by adding it to the $logs array.
  • The getLogs() method retrieves logs stored in the $logs array.


Flowchart: Singleton design pattern implementation.
Flowchart: Singleton design pattern implementation.

PHP Code Editor:

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