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copied!<p>There are a couple of ways of doing that. Global variables is certainly one way and the most looked down upon too. You can create a <a href="http://en.wikipedia.org/wiki/Singleton_pattern#PHP" rel="noreferrer" title="Singleton">Singleton</a> and all other classes that need database access would call upon this singleton.</p> <pre><code>final class Database { private static $connection; public static function getInstance() { if(self::$connection == NULL) { self::$connection = // init your database connection } return self::$connection; } } </code></pre> <p>And use this database connection object in whatever class needs it.</p> <pre><code>class Application { public function displayVar() { echo 'hello world'; } public function getVar() { $db = Database::getInstance(); $sql = foo; $db->query($sql); } } </code></pre> <p>This is all well for a start and a great step beyond using global variables, but you can do better with <a href="http://en.wikipedia.org/wiki/Dependency_injection" rel="noreferrer" title="Dependency Injection">Dependency Injection</a>. Dependency Injection is a simple concept that if a class has any external dependencies, such as the database connection in your example, you explicitly pass those to the needy class in its constructor or a method. So the new code would look something like Jonathan's solution. A major advantage of using dependency injection is in unit testing, where you can easily replace this actual database object with a mock object and pass it to whoever needs it.</p> <pre><code>class Application { private $db; public function __construct(Database $db) { $this->db = $db; } public function displayVar() { echo 'hello world'; } public function getVar() { $sql = foo; $this->db->query($sql); } } </code></pre> <p>For smaller projects, you can easily do it yourself. For large projects, there are various <a href="http://en.wikipedia.org/wiki/Dependency_injection#Existing_frameworks" rel="noreferrer" title="DI frameworks available for PHP">DI frameworks available for PHP</a></p>

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