singleton

问题 Closed . This question is opinion-based. It is not currently accepting answers. Want to improve this question? Update the question so it can be answered with facts and citations by editing this post. Closed 5 years ago . I have read a number of discussions on web and stack which claim singletons to be evil. Like: root-cause-of-singletons and Why is Singleton considered an anti-pattern? I read comments like "singletons make code complex, pain to reuse and test". I work with code that has

问题 It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center. Closed 7 years ago . I know about Singleton, but I can't use it in an Android project. I am a beginner in Android. Please tell me how & where we can use Singleton in an Android project for Large Data. I have used it for simple values

问题 It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center. Closed 7 years ago . I know about Singleton, but I can't use it in an Android project. I am a beginner in Android. Please tell me how & where we can use Singleton in an Android project for Large Data. I have used it for simple values

问题 As is now well known the recommended way for creating a singleton in java is via an enum (see for instance here) But (for example in this answer) it seems to be considered (by @MikeAdler who replied to me in the comments) the right thing to have the enum in the singleton class (see for instance here for a full example, or the code given below). I do not seem to really understand the need/use of this - can someone please elaborate (and preferably give the correct dialect for this idiom) ?

问题 As is now well known the recommended way for creating a singleton in java is via an enum (see for instance here) But (for example in this answer) it seems to be considered (by @MikeAdler who replied to me in the comments) the right thing to have the enum in the singleton class (see for instance here for a full example, or the code given below). I do not seem to really understand the need/use of this - can someone please elaborate (and preferably give the correct dialect for this idiom) ?

问题 In python, is it better that using the singleton pattern instead of using global variable? class Singleton(type): def __call__(self, *args, **kwargs): if 'instance' not in self.__dict__: self.instance = super(Singleton, self).__call__(*args, **kwargs) return self.instance or just make a global variable: SINGLETON_VARIABLE = None def getSingleton(): if SINGLETON is None: SINGLETON_VARIABLE = SOME_ININ_CLASS() return SINGLETON_VARIABLE Is it necessary to complicate the life to make a singleton

问题 I have an application that has several classes used for storing application-wide settings (locations of resources, user settings, and such). Right now these classes are just full of static fields and methods, but I never instantiate them. Someone suggested I make them Singletons, What's the case for/against? 回答1: Effective Java says: Singletons typically represent some system component that is intrinsically unique, such as a video display or file system. So if your component warrants single

问题 When can i cleanup objects stored in static variables in C#? I have a static variable that is lazily initialized: public class Sqm { private static Lazy<Sqm> _default = new Lazy<Sqm>(); public static Sqm Default { get { return _default.Value; } } } Note : That i've just changed Foo to be a static class. It doesn't change the question in any way if Foo is static or not. But some people are convinced that there is no way that an instance of Sqm could be constructed without first constructing an

问题 I've tried all the suggested solutions including: http://snehaprashant.blogspot.com/2009/01/singleton-pattern-in-java.html How to create a JVM-global Singleton? But none of these seem to work. They either are not truly Singletons across all ClassLoaders (the first link above) and result in different instances on application reload (I'm using Play Framework 1.3.x which reloads classes upon code change and recompile), or they require the classes to be on the System classpath. Is there a

问题 I have never done any Singleton class before and now I figured that for this DB connection it will be a good idea to make one, but I have no clue why it is not working. I really would appreciate if someone would help me out with this one since I want to learn how OOP works... Anyway, I fixed it with just updating my PHP to latest version, now $DBH = new static(); works fine, thanks people. I tried to use $DBH = new static(); isntead of $DBH = new self(); but then I have this error: Parse