What is Singleton Pattern?
Turkish: Singleton Deseni
The Singleton pattern ensures a class has one application-wide instance, centralizing access to shared resources or configuration.
What is the Singleton Pattern?
The Singleton pattern is an object-oriented design pattern that allows only one instance of a class to exist. Different parts of the application access the same instance, making configuration, logging, or a specific resource manager available from one central point.
A typical implementation hides the constructor, stores a single instance inside the class, and exposes a static method to access it. In some languages, module systems or dependency injection containers solve the same need more naturally.
Where Is It Used?
- Configuration: Reading application settings from one place.
- Logger: Sharing the same logging infrastructure across modules.
- Cache manager: Reusing a shared memory or connection object.
- Hardware or file lock: Limiting conflicting access to a single resource.
Things to Watch
Singleton can look convenient, but it creates global state and can make tests harder. Sequential tests may affect each other, parallel execution can expose thread-safety issues, and the code’s real dependencies may be hidden.
For that reason, Singleton should be understood as a design pattern, not used as the default answer for every shared object. In many applications, dependency injection manages lifecycle more explicitly and keeps code easier to test.
Related Terms
Dependency injection lets a class receive the dependencies it needs from the outside instead of constructing them itself.
Factory PatternThe Factory pattern moves object creation decisions into a producer component so client code stays independent of concrete classes.
Design PatternA design pattern describes a proven approach to recurring software design problems, independent of a specific language or framework.