singleton

问题 How does Java ensure internally that only one instance of an ENUM would exist per JVM? Is it created when application boots up and from that point on when multiple threads access it, it will just return the object created at startup? Or does it implement some kind of double synchronization similar to the singleton pattern so that even if multiple threads access it, only one istance will be created? 回答1: as you can read in this answer enum instances are static class fields and so are

问题 I have a repository manager that manages my repositories. I have the @Autowired to instantiate my properties, but they are always null. The beans are correctly configured in my xml. Any reason why? public class RepositoryManager { private static RepositoryManager instance; private RepositoryManager() { } public static RepositoryManager Instance() { if(instance == null) instance = new RepositoryManager(); return instance; } @Autowired private IUserRepository userRepository; @Autowired private

问题 So I am thinking about building a hobby project, one off kind of thing, just to brush up on my programming/design. It's basically a multi threaded web spider, updating the same data structure object->int. So it is definitely overkill to use a database for this, and the only thing I could think of is a thread-safe singleton used to contain my data structure. http://web.archive.org/web/20121106190537/http://www.ibm.com/developerworks/java/library/j-dcl/index.html Is there a different approach I

问题 Closed . This question needs to be more focused. It is not currently accepting answers. Want to improve this question? Update the question so it focuses on one problem only by editing this post. Closed 3 years ago . I would like to know, what are the principal differences between : javax.enterprise.context.SessionScoped and javax.ejb.Stateful javax.enterprise.context.ApplicationScoped and javax.ejb.Singleton I know that a @SessionScoped and a @Stateful allows to create a new instance for each

问题 This question already has answers here : What is an efficient way to implement a singleton pattern in Java? [closed] (29 answers) Closed 3 years ago . You know, that since Java 5 is released the recommended way to write Singleton pattern in Java is using enum. public enum Singleton { INSTANCE; } But, what I don't like in this - is to force the client to use Singleton.INSTANCE in order to have access to the singleton instance. Maybe, the better way to hide Singleton inside the ordinary class,

问题 I'm still confused a little with using Swift and was hoping that someone could help clarify when and why I would you them. From my understanding of Singleton's they are single class entities, meaning that if I have Class A and I create a shared instance of Class A in a Class B its just a reference to Class A in B, so if I change or modify the object that references Class A in Class B, the original object Class is is not effected, only the object in Class B is. What if I wanted to have a Class

问题 class Singleton(type): def __init__(self, *args, **kwargs): print 'calling __init__ of Singleton class', self print 'args: ', args print 'kwargs: ', kwargs super(Singleton, self).__init__(*args, **kwargs) self.__instance = None def __call__(self, *args, **kwargs): print 'running __call__ of Singleton', self print 'args: ', args print 'kwargs: ', kwargs, '\n\n' if self.__instance is None: self.__instance = super(Singleton, self).__call__(*args, **kwargs) return self.__instance class A(object):

问题 Generally, I like to keep an application completely ignorant of the IoC container. However I have ran into problems where I needed to access it. To abstract away the pain I use a basic Singleton. Before you run for the hills or pull out the shotgun, let me go over my solution. Basically, the IoC singleton does absolutly nothing, it simply delegates to an internal interface that must be passed in. I've found this makes working with the Singleton less painful. Below is the IoC wrapper: public

问题 i have implemented a singleton (static version) in C++. I know all the controversy about this pattern and potential thread-safety issues, but i am curious why this exact implementation won't halt. The program never quits, it remains in a deadlock state at the end. singleton.h: #pragma once #include <thread> #include <atomic> class Singleton { public: static Singleton& getInstance(); private: std::thread mThread; std::atomic_bool mRun; Singleton(); ~Singleton(); void threadFoo(); }; singleton

问题 This seems like a simple thing that most people would need if they wanted to use Google Plus sign in with their application :s. In Activity 1: I sign the user in. After the sign in, I want to make that user object globally accessible, so I add it to the Application object: public class GlobalUserAccess extends Application { private GoogleApiClient mGoogleApiClient; public GlobalUserAccess(){ mGoogleApiClient = null; } public void setClient(GoogleApiClient client){ mGoogleApiClient = client; }