Singleton is a creational design pattern that ensures a class has only one instance and provides a global access point to that instance.
Problem
In software development, it’s common to need a single instance of a class to be shared across an application. Having multiple instances can lead to issues such as unexpected behaviors or inefficient resource usage.
Solution
The Singleton pattern addresses this problem by:
- Making the class constructor private to prevent direct instantiation from outside the class.
- Providing a static public method that acts as a constructor. Before creating a new instance, it checks if an instance already exists in a private static field. If the field is
null
, it creates a new instance and assigns it to the field; otherwise, it returns the existing instance.
Java example
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Applications
Use the Singleton pattern when you need a single instance of a class to be shared across the entire application.
Tips
- Be careful when using the Singleton pattern in multi-threaded scenarios, as it is not inherently thread-safe. Check this article for further details