Design Patterns

A solid reference for the patterns you actually use: Factory, Builder, Strategy, Observer, and the rest. It shows both the classic Java approach and modern alternatives with Spring and Lombok, which is helpful since you probably don't want to write boilerplate builders by hand in 2024. The examples are practical, like swapping payment methods at runtime with Strategy or avoiding telescoping constructors with Builder. It's opinionated in the right ways, steering you toward dependency injection over Singleton and showing antipatterns alongside solutions. Best for when you know a pattern would help but can't remember the exact implementation, or when you're teaching someone why their seven-parameter constructor is a code smell.

skills.sh installs: 372
GitHub stars: 771
last updated: Feb 8, 2026

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Install

$ npx -y skills add decebals/claude-code-java --skill design-patterns --agent claude-code

Installs into .claude/skills of the current project.

Files

Design Patterns Skill

Practical design patterns reference for Java with modern examples.

When to Use

User asks to implement a specific pattern
Designing extensible/flexible components
Refactoring rigid code structures
Code review suggests pattern usage

Quick Reference: When to Use What

Problem	Pattern
Complex object construction	Builder
Create objects without specifying class	Factory
Multiple algorithms, swap at runtime	Strategy
Add behavior without changing class	Decorator
Notify multiple objects of changes	Observer
Ensure single instance	Singleton
Convert incompatible interfaces	Adapter
Define algorithm skeleton	Template Method

Creational Patterns

Builder

Use when: Object has many parameters, some optional.

// ❌ Telescoping constructor antipattern
public class User {
    public User(String name) { }
    public User(String name, String email) { }
    public User(String name, String email, int age) { }
    public User(String name, String email, int age, String phone) { }
    // ... explosion of constructors
}

SKILL.md on GitHub