PHP Class: Singleton design pattern implementation

Last update on May 29 2025 13:10:22 (UTC/GMT +8 hours)

18. Logger with Singleton Design Pattern

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 :

<?php
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

Explanation:

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:

For more Practice: Solve these Related Problems:

Write a PHP class Logger that implements the singleton pattern and demonstrates logging of multiple events via a single instance.
Write a PHP script to create multiple references to the Logger singleton and verify that all log messages are consolidated.
Write a PHP function to reset the Logger instance and output a log message confirming the singleton behavior.
Write a PHP program to test concurrent access to the Logger singleton and ensure thread-safe logging operations.

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