Singleton restricts the instantiation of a class to only a single object instance.
The singleton pattern makes sure that a given class has always only one living instance in the application. This can be used, for example, when you want to restrict resource access to one and only one memory context in the process. For instance, a database connector class can be a singleton that deals with synchronization and manages its data in memory. It makes the assumption that no other instance is interacting with the database in the meantime.
This pattern can simplify a lot of the way that concurrency is handled in an application. Utilities that provide application-wide functions are often declared singletons. For instance, in web applications, ...
