Creating Singleton Class in php

The Singleton Pattern is one of the GoF (Gang of Four) Patterns. This particular pattern provides a method for limiting the number of instances of an object to just one. It's an easy pattern to grasp once you get past the strange syntax used.

class Database
{
    // Store the single instance of Database
    private static $m_pInstance; //must be private instance variable
    private $count = 0;
    
    private function __construct() //must be private constructor
    { 
        echo "creating database connetion <br />";

    }

    public static function getInstance()
    {
        if (!self::$m_pInstance)
        {
            self::$m_pInstance = new Database();
        }
        return self::$m_pInstance;
    }

    public function query($query)
    {
        echo $query."<br />";
    }

    public function increment()
    {
        return $this->count++;
    }

}

//Singleton way
for($n=1;$n<5;$n++){
    $pDatabase = Database::getInstance(); //the object will be initiated only once
    $aResult = $pDatabase->query('executing query in singleton');
    echo $pDatabase->increment()."<br />";
    echo $pDatabase->increment()."<br />";
    echo $pDatabase->increment()."<br />";
}


echo "<hr />";

//Usual way
for($n=1;$n<5;$n++){
    $pDatabase = new Database(); //error - change constructior to public to fix
    $aResult = $pDatabase->query('executing query in usual way');
    echo $pDatabase->increment()."<br />";
    echo $pDatabase->increment()."<br />";
    echo $pDatabase->increment()."<br />";
}

Thowfeek M. Khan

Creating Singleton Class in php