singleton

问题 Edit: Answered - error was method wasn't static I'm used the Singleton Design Pattern public class Singleton { private static final Singleton INSTANCE = new Singleton(); // Private constructor prevents instantiation from other classes private Singleton() {} public static Singleton getInstance() { return INSTANCE; } } My question is how do I create an object of class Singleton in another class? I've tried: Singleton singleton = new Singleton(); // error - constructor is private Singleton

问题 Just want to make sure I am not assuming something foolish here, when implementing the singleton pattern in an ASP .Net web application the static variable scope is only for the current user session, right? If a second user is accessing the site it is a different memory scope...? 回答1: The static variable scope is for the entire app domain, which means other sessions also have access to it. Only if you have a farm with different servers you would have more than one instance of the variable.

问题 the lazy thread-safe singleton instantion is kinda not easy to understand to every coder, so i wanted to create a class in our enterprise framework that would do the job. What do you think about it? Do you see something bad about it? Is there something similar like in Apache Commons? How can i make it better? Supplier.java public interface Supplier<T> { public T get(); } LazyThreadSafeInstantiator.java public class LazyThreadSafeInstantiator<T> implements Supplier<T> { private final Supplier

问题 I am making an object of AppDelegate and using it throughout my program, and I have declared all setters and getters, and also insert, select, delete, update queries of database in it. I want to ask that is it a good practice to do so, if yes, then how, and if no then why it is not a good practice? I hope my question is clear, please ask relating questions if you have any. 回答1: It's not a good strategy to turn your AppDelegate into a "big ball of mud" that contains a million methods and

问题 Why can't I do this in PHP? Where Database is a singleton class and getInstance() returns a PDO object. <?php class AnExample { protected static $db = Database::getInstance(); public static function doSomeQuery() { $stmt = static::$db->query("SELECT * FROM blah"); return $stmt->fetch(); } } Like any other PHP static variable, static properties may only be initialized using a literal or constant; expressions are not allowed. So while you may initialize a static property to an integer or array

问题 The Static Vs. Singleton question has been discussed before many times in SO. However, all the answers pointed out the many advantages of a singleton. My question is - what are the advantages of a static class over a singleton? Why not simply choose a singleton every time? 回答1: Static class is a technical tool in your box - basically a language feature. Singleton is an architectural concept. You may use a static class as a means to implement the singleton concept. Or you may use some other

问题 A few days ago, I had an issue with ASP.Net threading. I wanted to have a singleton object per web request. I actually need this for my unit of work. I wanted to instantiate a unit of work per web request so that identity map is valid through out the request. This way I could use an IoC to inject my own IUnitOfWork to my repository classes transparently, and I could use the same instance to query and then update my entities. Since I am using Unity, I mistakenly used PerThreadLifeTimeManager.

问题 I've been trying to implement a singleton to be used as a cache for photos which I uploaded to my iOS app from the web. I've attached three variants in the code below. I tried to get variant 2 working but it is causing a compiler error which I do not understand and would like to get help on what am I doing wrong. Variant 1 does the caching but I do not like the use of a global variable. Variant 3 does not do the actual caching and I believe it is because I am getting a copy in the assignment

问题 I understand that double locking in Java is broken, so what are the best ways to make Singletons Thread Safe in Java? The first thing that springs to my mind is: class Singleton{ private static Singleton instance; private Singleton(){} public static synchronized Singleton getInstance(){ if(instance == null) instance = new Singleton(); return instance; } } Does this work? if so, is it the best way (I guess that depends on circumstances, so stating when a particular technique is best, would be

问题 I understand that double locking in Java is broken, so what are the best ways to make Singletons Thread Safe in Java? The first thing that springs to my mind is: class Singleton{ private static Singleton instance; private Singleton(){} public static synchronized Singleton getInstance(){ if(instance == null) instance = new Singleton(); return instance; } } Does this work? if so, is it the best way (I guess that depends on circumstances, so stating when a particular technique is best, would be