Complete runnable Java 17 implementations of all 23 Gang of Four design patterns. Each pattern has a dedicated article at ankurm.com with a UML diagram, step-by-step explanation, and console output.

Structure

design-patterns/
├── 01-creational/
│   ├── factory-method/
│   ├── abstract-factory/
│   ├── builder/
│   ├── prototype/
│   └── singleton/
├── 02-structural/
│   ├── adapter/
│   ├── bridge/
│   ├── composite/
│   ├── decorator/
│   ├── facade/
│   ├── flyweight/
│   └── proxy/
└── 03-behavioral/
    ├── chain-of-responsibility/
    ├── command/
    ├── interpreter/
    ├── iterator/
    ├── mediator/
    ├── memento/
    ├── observer/
    ├── state/
    ├── strategy/
    ├── template-method/
    └── visitor/

Prerequisites

Java 17+ (Eclipse Temurin recommended)
No build tool required — plain javac / java

Run any pattern

# Windows (PowerShell)
$JAVAC = 'C:\Program Files\Eclipse Adoptium\jdk-17.0.7.7-hotspot\bin\javac.exe'
$JAVA  = 'C:\Program Files\Eclipse Adoptium\jdk-17.0.7.7-hotspot\bin\java.exe'

& $JAVAC 03-behavioral/strategy/*.java -d out/strategy
& $JAVA -cp out/strategy strategy.Main

# Linux / macOS
javac 03-behavioral/strategy/*.java -d out/strategy
java -cp out/strategy strategy.Main

Run all behavioral patterns (Windows)

Double-click RUN-behavioral.bat or run in PowerShell:

powershell -ExecutionPolicy Bypass -File run-behavioral.ps1

Articles

Pattern	Category	Article
Factory Method	Creational	https://ankurm.com/factory-method-design-pattern-java/
Abstract Factory	Creational	https://ankurm.com/abstract-factory-design-pattern-java/
Builder	Creational	https://ankurm.com/builder-design-pattern-java/
Prototype	Creational	https://ankurm.com/prototype-design-pattern-java/
Singleton	Creational	https://ankurm.com/singleton-design-pattern-java/
Adapter	Structural	https://ankurm.com/adapter-design-pattern-java/
Bridge	Structural	https://ankurm.com/bridge-design-pattern-java/
Composite	Structural	https://ankurm.com/composite-design-pattern-java/
Decorator	Structural	https://ankurm.com/decorator-design-pattern-java/
Facade	Structural	https://ankurm.com/facade-design-pattern-java/
Flyweight	Structural	https://ankurm.com/flyweight-design-pattern-java/
Proxy	Structural	https://ankurm.com/proxy-design-pattern-java/
Chain of Responsibility	Behavioral	https://ankurm.com/chain-of-responsibility-design-pattern-java/
Command	Behavioral	https://ankurm.com/command-design-pattern-java/
Interpreter	Behavioral	https://ankurm.com/interpreter-design-pattern-java/
Iterator	Behavioral	https://ankurm.com/iterator-design-pattern-java/
Mediator	Behavioral	https://ankurm.com/mediator-design-pattern-java/
Memento	Behavioral	https://ankurm.com/memento-design-pattern-java/
Observer	Behavioral	https://ankurm.com/observer-design-pattern-java/
State	Behavioral	https://ankurm.com/state-design-pattern-java/
Strategy	Behavioral	https://ankurm.com/strategy-design-pattern-java/
Template Method	Behavioral	https://ankurm.com/template-method-design-pattern-java/
Visitor	Behavioral	https://ankurm.com/visitor-design-pattern-java/

Reference

Design Patterns: Elements of Reusable Object-Oriented Software — Gamma, Helm, Johnson, Vlissides
https://refactoring.guru/design-patterns