public class NameOfClass
{	
	private static var NameOfClass;
		 
	public function NameOfClass(s:Singelton) 
        { 
          
        }
		
	public static function getInstance():NameOfClass
	{
		if (!NameOfClass._instance)
		{
			NameOfClass._instance = new NameOfClass(new Singelton());
		}
			
		return NameOfClass._instance;
	}
}internal class Singelton {}

A singleton class

Singelton Class

ActionScript 3