function getInstance(){
if(! self::$_instance){
self::$_instance=new self;
}
return self::$_instance;
}

function __construct(){

}

function Show(){
echo 'Singleton on Php5';
}
}

{
$Singleton=SingletonPhp5::getInstance()->Show();
}

class SingletonPhp4{
function &getInstance(){
static $_instance=array();
if(empty($_instance)){
$_instance[]= & new SingletonPhp4();

}
return $_instance[0];

}

function SingletonPhp4(){

}

function Show(){
echo 'Singleton on Php4';
}
}

{
$Singleton=SingletonPhp4::getInstance();
$Singleton->Show();
}