The private field can be assigned from within a static initializer block or, more simply, using an initializer. The getInstance method which must be public then simply returns this instance. Using this class is equally simple: However, it is clear that a class with only a private constructor cannot be subclassed, so this paranoia does not appear to be necessary.
You want the Singleton pattern. There is an excellent discussion of how to implement this properly. If you do this right, there will only ever be one instance of the class. Essentially what you are going to do is create a class, hold a single instantiated object of that class at the static level, and provide a static accessor to get it getInstance or similar.
Make the constructor final so people can't create their own instances out of the blue. That link above has plenty of great advice on how to do this. But in literature, a Singleton is in general considered to be a bad design idea. Of course this always somewhat depends on the situation, but most programmers advice against it. Only saying it, don't shoot on the messenger Considering a class A that you only wish to have one of, then an alternative is to have a builder or factory class that itself limits the creation of the number of objects of Class A, and that could be by a simple counter.
The advantage is that Class A no longer needs to worry about that, it concentrates on its real purpose. Every class that uses it no longer has to worry about it being a singleton either no more getInstance calls. Use enum.
How to make sure that there is just one instance of class in JVM? Ask Question. Joe Joe 2 9 Your question is confusing, but you can enforce Singleton Pattern to make sure only one instance is created. There's an argument that says you should reconsider this design. Google has implemented a Singleton Detector to make sure people don't use them in applications: Clusters won't honor your wish, either.
Joe, you can create a Singleton, but if you want it to be shared dhaka university natok all the classloaders in the JVM, you can checkout this thread: John Kugelman k 54 Sufiyan Ghori Sufiyan Ghori Instead of throwing an exception while cloning, you could return this?
Actually, the easiest implementation of a singleton, since Java 1. There's a way to add that to your implementation, with enough effort. Josh Bloch in the updated edition of Effective Java recommends using enums in this way. What's the advantage of using singletons over static methods in a class with a private constructor? Todd Todd Plus one for linking to that discussion. The idea of using an enum is just brilliant IMO. ApproachingDarknessFish Yes, I agree, it's a very nice method for doing it.
That's the well known Singleton pattern: There is a school of thought that considers the Singleton pattern to in fact be an anti-pattern. Jool Jool 1, 10 9. Also - side effects. Implementing Singleton with an Enum in Java Discussion: Vlad Lifliand Vlad Lifliand 2 5.
Stephen C Stephen C k 70 Ravindra babu Ravindra babu If I want only one object for this Connect class: Kroltan 3, 2 27 Chandan Rajput Chandan Rajput Why do you make this volatile and do you use synchronized? By simply using a field initializer, this is all handled correctly. Although I don't see why one needs to make it that compilcated CommuSoft - Just wait 'till you hit a threading issue, see how difficult it will be to track down the problem.
It's not complicated if you ue an enum or a static initialiser. Also, using synchronized on the Class is dangerous because another tool could also synchronize on your class a cause deadlock. Pehlaj 6, 7 27 While your code may provide a solution to the OP's issue, please ensure you explain your code clearly.
You can learn more about it by perusing SitePoint articles on the subject. Usually, the goal is to manage global application state.
When that code is interpreted, UserStore will be set to the result of that immediately invoked function — an object that exposes two functions, but that does not grant direct access to the collection of data. Code executed later could modify either one of the exposed functions, or even redefine UserStore altogether. If we got bugs as a result of unexpected modification of UsersStoretracking them down in a larger project could prove very frustrating.
There are more advanced moves you could pull to mitigate some of these downsides, as specified in this article by Ben Cherry. His goal is to create modules, which just happen to be singletons, but the pattern is the same.
But if you can see holes in it, please let me know. Also please advocate for whichever of the new patterns you prefer, and whether or not you think object literals are the way to go, or if you prefer classes! Login Sign Up.