Singleton Pattern

Status: draft · Confidence: medium (0.635) · Basis: verified_sources

Quality notes: generic_source_homepage, no_verified_sources, partial_source_verification

## TL;DR

Ensures a class has only one instance and provides global access. Used for shared resources: database connections, config, logging. Modern criticism: hidden global state, testing difficulty.

## Core Explanation

Implementation: private constructor, static getInstance(). Thread-safe: double-checked locking, static initializer, or enum (Java). In JavaScript: module-level variable (modules are singletons by default). Dependency injection is often preferred over Singleton today.

## Further Reading

- [Design Patterns (Gang of Four)](undefined)

## Related Articles

- [Adapter Pattern](../adapter-pattern.md)
- [Command Pattern](../command-pattern.md)
- [Decorator Pattern](../decorator-pattern.md)