What are the difference between a Static class and a Singleton class?

Static Class:

  • A static class is a class that cannot be instantiated and is designed to provide utility or helper functions or to group related methods together.
  • All members (fields, methods) of a static class must be declared as static.
  • Static classes are accessed directly using the class name, without the need to create an instance of the class.
  • Static classes are often used to organize and encapsulate related methods or functions that do not require instance-level state or access to instance-specific data.
  • Static classes cannot be subclassed or inherited from.

Singleton Class:

  • A singleton class is a class that allows only a single instance of itself to be created and provides a global point of access to that instance.
  • The purpose of a singleton class is to ensure that there is only one instance of the class throughout the application.
  • Singleton classes typically have a private constructor to prevent direct instantiation and provide a static method (often called getInstance()) to access the single instance.
  • Singleton classes may hold state or data that is shared across multiple parts of the application.
  • Singleton classes are accessed through their instance by calling the static method getInstance().
  • Singleton classes can be subclassed, but the subclassing may affect the uniqueness of the single instance, and careful consideration is required when implementing inheritance with singleton classes.

Key Differences:

  1. Instantiation: Static classes cannot be instantiated, while singleton classes allow the creation of a single instance.
  2. Accessibility: Static class members are accessed directly using the class name, while singleton instances are accessed through the static getInstance() method.
  3. Multiple Instances: Static classes cannot have instances at all, while singleton classes have only one instance throughout the application.
  4. Subclassing: Static classes cannot be subclassed, while singleton classes can be subclassed, although it may affect the uniqueness of the single instance.
  5. Purpose: Static classes are used for grouping related methods or providing utility functions, while singleton classes are used when there should be only one instance of a class, often with shared state or functionality.
  6. Design Intent: Static classes focus on organizing and encapsulating related functionality, while singleton classes focus on ensuring a single point of access to a shared instance.

It’s important to note that static classes and singleton classes serve different purposes and should be chosen based on the specific requirements of the application or problem domain.

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