A conceptual blueprint (it is an idea)

• A proven, reusable solution to a recurring software design problem, at the design level, not code level.
• Not a library / framework / specific code
• ✅ Loose coupling
• ✅ Open/Closed Principle
• ✅ Scalability
• ✅ Maintainability
• ✅ Testability

CREATIONAL PATTERNS (Object creation)

1. Singleton

• Private constructor
  • Cannot create extra instance
• Static final instance
  • Global access point
  • thread safe
  • JVM guarantees initialization once
• Public access method
• Real-world usage:
  • Spring beans (by default)
  • Logger
  • Cache manager

public class ConfigManager {
    private static final ConfigManager INSTANCE = new ConfigManager();

    private ConfigManager() {}

    public static ConfigManager getInstance() {
        return INSTANCE;
    }
}

Singleton ≠ global variable

Singleton controls creation + lifecycle