---
id:"kb-2026-00141"
title:"Singleton Pattern"
schema_type:"TechArticle"
category:"computer-science"
language:"en"
confidence:"high"
last_verified:"2026-05-22"
generation_method: "human_only"
ai_models:["claude-opus"]
derived_from_human_seed:true


known_gaps:
  - "Sources reconstructed during quality audit; primary source details were corrupted during batch generation"

completeness: 0.88
ai_citations:
  last_citation_check:"2026-05-22"
primary_sources:
- title: "ACM Digital Library"
    type: "repository"
    year: 2026
    url: "https://dl.acm.org/"
    institution: "ACM"
secondary_sources:
  - title: "ACM Digital Library"
    type: "repository"
    year: 2026
    url: "https://dl.acm.org/"
    institution: "ACM"
---

## 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)