Singleton Design Pattern 🧩

The Singleton Pattern is a creational design pattern that ensures a class has only one instance and provides a global point of access to it. It's commonly used when exactly one object needs to coordinate actions across a system, such as managing database connections or configuration settings.

Key Concepts 🔍

• Lazy Initialization: Creates the instance only when needed
• Eager Initialization: Initializes the instance at startup
• Thread Safety: Requires careful handling in multi-threaded environments
• Static Factory Method: Often used to implement the pattern

Implementation Examples 📜

// Eager Initialization
public class EagerSingleton {
    private static final EagerSingleton instance = new EagerSingleton();
    private EagerSingleton() {}
    public static EagerSingleton getInstance() {
        return instance;
    }
}

// Lazy Initialization with Double-Check Locking
public class LazySingleton {
    private static volatile LazySingleton instance;
    private LazySingleton() {}
    public static LazySingleton getInstance() {
        if (instance == null) {
            synchronized (LazySingleton.class) {
                if (instance == null) {
                    instance = new LazySingleton();
                }
            }
        }
        return instance;
    }
}

Common Use Cases 📈

• Database Connection Pool
• Configuration Manager
• Logging Systems
• Session Management

Pros & Cons ⚖️

✅ Advantages:

• Centralized control of resources
• Avoids redundant object creation

❌ Disadvantages:

• Can make testing difficult
• Violates the Single Responsibility Principle in some cases

Further Reading 📚

For a deeper dive into other design patterns, check out:
/[[en/videos/advanced/java/oop/design_patterns/factory]]