What makes the Singleton pattern so popular and in what cases is it used?

The Singleton pattern is popular because it guarantees that only one instance of a class exists in the application and provides a global access point to that instance. This is convenient when a shared resource or state is needed, such as configuration, connection pool, or logger.

Main reasons for popularity:

• Control over instance creation (single object)
• Global accessibility
• Resource savings

Singleton is used when:

• Centralized management of state is required
• The object is heavy to create, and repeated creation is undesirable
• A single data source or service is needed

Example of Singleton implementation in Java:

public class Singleton {
    private static Singleton instance;

    private Singleton() {
        // private constructor
    }

    public static synchronized Singleton getInstance() {
        if (instance == null) {
            instance = new Singleton();
        }
        return instance;
    }
}

It is important to consider that in a multithreaded environment, thread safety must be ensured during instance creation.