What are some specific legitimate uses for singletons? [duplicate]

Answer 1

We basically use them for two things: logging, and configuration. Both assume that the app has a central config and a central logfile, not always valid but in most of our code it is. We also use them on occasion for certain factory classes or cache classes we want to make sure we're not duplicating key metadata.

Answer 2

Master server takes requests from clients, and passes these requests off to a subordinate process. The subordinate process may use a singleton for communicating with the master server.

Answer 3

There is a single device/hardware attached to the system and a central point of control is necessary in order to use it properly.

Answer 4

• Logging.

• Finding localized string resources e.g. Strings.get("CONFIRM_DELETE").

Both of these things are not details that should be exposed in the public interface of your objects, so it makes sense to use a singleton here.

Answer 5

When a part of your program needs an object that implements a specific interface (polymorphism-wise), but you never want more than a single instance of that object. Otherwise static methods will do.

Answer 6

Generating a sequence of random numbers - the random generator should be unique, not instantiated for each use. One might want to implement this as a thread-level singleton; however, a singleton for the whole process is still appropriate in this case.