Prabod's Tech Blog: Singleton Design Pattern

What is Singleton Design Pattern?

A class must ensure that only one single instance should be created and that single object can be used by all other classes.

Save memory because an object is not created each request. Only one instance is using every time.

This pattern is mostly using in multi-threaded and database applications. It is using in logging, caching, thread pools, configuration settings, etc.

To create a singleton class, we need to have static member of class, private constructor and factory method.

Static member: It gets memory only once because of static, it contains the instance of the singleton class.
Private constructor: It will prevent to instantiate the singleton class from outside the class.
Static factory method: This provides access to the singleton object and returns the instance to the caller.

Create the instance of the class at the time of declaring the static member, so the instance of the class is created at the time of class loading.

Create the instance of the class in a synchronized method or synchronized block, so the instance of the class is created when required