singleton

问题 Good day, friends. Once again stupid question about Obj-C from newbie :) I'm trying to implement singleton design pattern in Obj-C: @interface SampleSingleton : NSObject { @private static SampleSingleton* instance; } +(SampleSingleton*) getInstance; Compiler returns error: "expected specifier-qualifier-list before 'static'". 回答1: Please find below the Objective-C code snippet I am using, for proper thread-safe singleton implementation header file : /* * * Singleton interface that match Cocoa

问题 I have created a singleton class and I want to create a class which is subclass of this singleton class, what is the correct method to do it 回答1: I don't know about Objective-C in particular, but in general singleton classes should prevent subclassing. If you've got an instance of the base class and an instance of the subclass, then you've effectively got two objects you can regard as instances of the base "singleton" class, haven't you? As soon as you've got two instances, it's not really a

问题 Normally in a sprite kit game, when a new scene presented, all the nodes in the old scene and their content removed automatically. Now what is, if a node like "HUD" should be not removed? Is there any way in sprite kit to create a node only once and use it in all scenes without removing and creating it again and again every time in every new scene? There must be a technique that makes it possible. that's a serious sprite kit design problem, if it is not possible. But I don't think so. The

问题 I believe Jimmy Nillson said he generally made his webservices singletons. Is this the preferred method, and with WCF? Other than making the service methods static, is there something else to be done? 回答1: good responses, but I think there is a problem in the original question. "Typical use" of a technology is a poorly formed question. No one has a "typical" scenario, and you should review the requirements of your particular problem before deciding on an implementation or approach. Your

问题 Below show is the creation on the singleton object. public class Map_en_US extends mapTree { private static Map_en_US m_instance; private Map_en_US() {} static{ m_instance = new Map_en_US(); m_instance.init(); } public static Map_en_US getInstance(){ return m_instance; } @Override protected void init() { //some code; } } My question is what is the reason for using a static block for instantiating. i am familiar with below form of instantiation of the singleton. public static Map_en_US

问题 I want to know when should i exactly use the prototype scope in Spring? I have understood that singleton returns the same object instance if the bean is requested for. Then why should we consider prototype ? Explanations with examples would help a lot to understand the need for it. 回答1: To be clear simple definitions: Prototype scope = A new object is created each time it is injected/looked up. It will use new SomeBean() each time. Singleton scope = The same object is returned each time it is

问题 I've tried a few times to understand what a Singleton is. Perhaps I'm just too visual.. so can anyone break it down in a simple analogy. Similar Posts: Different ways to initialize singletons Singleton: How should it be used Is this a good use of the Singleton pattern? What is so bad about singletons? Singleton: How should it be used Singletons: good design or a crutch? Global vs Singleton in .NET On Design Patterns: When to use the Singleton? Singleton with Arguments in Java What is an

问题 What is the best strategy to refactor a Singleton object to a cluster environment? We use Singleton to cache some custom information from Database. Its mostly read-only but gets refreshed when some particular event occurs. Now our application needs to be deployed in a Clustered environment. By definition, each JVM will have its own Singleton instance. So the cache may be out-of-sync between the JVM's when a refresh event occurs on a single node and its cache is refreshed. What is the best way

问题 I have a situation in which I'm asked to read collections of database update instructions from a variety of sources. All sources will contain a primary key value so that the code that applies the updates to the database can find the correct record. The files will vary, however, in what additional columns are reported. When I read and create my update instructions I must differentiate between an update in which a column (for instance, MiddleName) was provided but was empty (meaning no middle

问题 The fallowing clause is taken from jetbrains.net After reading this and some other articles on the web, I still don't understand how is it possible to return null, after the first thread go in to the lock. Some one that does understand it can please help me and explain it in more humanized way? "Consider the following piece of code: public class Foo { private static Foo instance; private static readonly object padlock = new object(); public static Foo Get() { if (instance == null) { lock