design-patterns

name	design-patterns
description	Common design patterns with Java examples (Factory, Builder, Strategy, Observer, Decorator, etc.). Use when user asks "implement pattern", "use factory", "strategy pattern", or when designing extensible components.

Design Patterns Skill

Quick reference for common design patterns in Java.

When to Use

• User asks to implement a specific pattern
• Designing extensible/flexible components
• Refactoring rigid code

Quick Reference: When to Use What

Problem	Pattern	Use When
Complex object construction	Builder	Many parameters, some optional
Create objects without specifying class	Factory	Type determined at runtime
Multiple algorithms, swap at runtime	Strategy	Behavior varies by context
Add behavior without changing class	Decorator	Dynamic composition needed
Notify multiple objects of changes	Observer	One-to-many dependency
Convert incompatible interfaces	Adapter	Integrate legacy/3rd party code

---

Creational Patterns

Builder

Problem: Telescoping constructors, many optional parameters

// ✅ Builder pattern
public class User {
      String name;  
      String email; 
       age;      

      {
        .name = builder.name;
        .email = builder.email;
        .age = builder.age;
    }

      Builder  {
          (name, email);
    }

        {
          String name;
          String email;
            ;

          {
            .name = name;
            .email = email;
        }

         Builder  {
            .age = age;
             ;
        }

         User  {
              ();
        }
    }
}


   User.builder(, )
    .age()
    .build();