asmhatre/design-patterns
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Add per-pattern README.md for the 5 creational patterns (Factory Method, Abstract Factory, Builder, Prototype, Singleton) for consistency with all other 18 patterns

Browse Source
This commit is contained in:
Ankur
2026-06-24 17:43:51 +05:30
parent ba4d142be2
commit 98ea39e084
5 changed files with 161 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

34
01-creational/singleton/README.md Normal file
View File

@@ -0,0 +1,34 @@
# Singleton Design Pattern — Java Example
**Pattern:** Creational → Singleton
**Article:** https://ankurm.com/singleton-design-pattern-java/
## What this example shows
Six different ways to implement a singleton, compiled and run side by side so their tradeoffs are directly comparable. `AppConfigEager` initializes at class-load time. `AppConfigNaiveLazy` defers initialization but is not thread-safe. `AppConfigSynchronized` fixes thread-safety at the cost of locking on every call. `AppConfigDCL` uses double-checked locking to avoid that per-call lock. `AppConfigHolder` uses the initialization-on-demand holder idiom for lazy, thread-safe initialization with no locking at all. `AppConfigEnum` uses a single-element enum, which the JVM guarantees is a singleton even against reflection and serialization attacks. `Main` exercises all six in one run.
## How to run
```bash
javac singleton/*.java -d out/singleton
java -cp out/singleton singleton.Main
```
Requires Java 25.
## Post Section ↔ File Mapping
| Post Section | File(s) |
|---|---|
| Implementation 1 — Eager Initialization | `AppConfigEager.java` |
| Implementation 2 — Naïve Lazy Initialization | `AppConfigNaiveLazy.java` |
| Implementation 3 — Synchronized Method | `AppConfigSynchronized.java` |
| Implementation 4 — Double-Checked Locking | `AppConfigDCL.java` |
| Implementation 5 — Initialization-on-Demand Holder | `AppConfigHolder.java` |
| Implementation 6 — Enum Singleton | `AppConfigEnum.java` |
| Running All Six Implementations Together | `Main.java` |
Each implementation is renamed to its own class (e.g. `AppConfigEager`, `AppConfigHolder`) so all six can be compiled together in one package and compared directly. The "Breaking via Reflection," "Breaking via Serialization," and Spring `@Component` snippets are illustrative only — they are not part of this repository's runnable example.
Article: https://ankurm.com/singleton-design-pattern-java/
All patterns: https://ankurm.com/design-patterns-java/