Why singleton pattern is used

As you were asking about a real world example, here we go. A few days ago, I had to implement holding a list of loaded assemblies and its references during program-execution. As this is a bigger project, we're talking about dll-files to look at. In that case, I just didn't want to load the same data again and again whenever I need to get one of these assemblies.

Therefore, I used a singleton-class, which creates this certain list on its first call and holds that values until the application gets closed. The singleton pattern can be used for anything that you don't want to repeat.

If the object in question is not expected to change, it is a good candidate for the singleton pattern. The singleton pattern is preferred over a static implementation in most cases. Static implementations can cause dependency headaches.

Can you provide more specifics as to what exactly you're looking to do? Hi, You can use it in remoting when you want to create a shareable service Thanks Robert I got your point..

Apr 15, Stay Inspired! Join other developers and designers who have already signed up for our mailing list. Made with in Austin, Texas. Vsn 1. Views: No interfaces, no inheritance, nothing fancy but ensuring that an attribute for holding a class instance and method for accessing that instance. In the code above, you may notice several oddities characterized by static methods, private constructors, and Factory-Pattern-like instantiation. These are the basic requirements for the Singleton pattern to ensure it behaves as intended.

This is a strange combination—given that static accessors are generally defined as public and would default to package-private if no accessor were specified the same as classes in Java. The use of a private static variable here ensures that only the Singleton class has access. Instead, the privatization of the constructor ensures only the Singleton class can create a new instance—with full control of the means of how such is done. This is the heart and soul of the Singleton and determines when to create a new Singleton instance and when to return an existing one.

If another class instance calls the getInstance method it will be given the existing Singleton instance, if it exists, or will trigger the Singleton class to create a new class instance and return that. With a few additions to the code above we can see how the Singleton class behaves. Consider the following additions:. This message is accessed via standard getter and setter methods. We can demonstrate the functionality of the class with the following code:.

On line one, we see the default message encoded into the Singleton class. Suppose an application where the logging utility has to produce one log file based on the messages received from the users.

If there is multiple client application using this logging utility class they might create multiple instances of this class and it can potentially cause issues during concurrent access to the same logger file. We can use the logger utility class as a singleton and provide a global point of reference so that each user can use this utility and no 2 users access it at the same time.

Configuration File: This is another potential candidate for Singleton pattern because this has a performance benefit as it prevents multiple users to repeatedly access and read the configuration file or properties file. It creates a single instance of the configuration file which can be accessed by multiple calls concurrently as it will provide static config data loaded into in-memory objects. The application only reads from the configuration file for the first time and thereafter from second call onwards the client applications read the data from in-memory objects.

Cache: We can use the cache as a singleton object as it can have a global point of reference and for all future calls to the cache object the client application will use the in-memory object. Important points Singleton classes can have only one instance and that instance should be globally accessible. Runtime and java. Desktop are 2 singleton classes provided by JVM.

Singleton Design pattern is a type of creational design pattern. Outer classes should be prevented to create instance of singleton class. If you like GeeksforGeeks and would like to contribute, you can also write an article using write. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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