🧠 Understanding Design Patterns in Java

🌟 What are Design Patterns?

In software development, Design Patterns are well-proven solutions to common software design problems.
They are reusable templates that can be applied to recurring situations when designing software systems.

Think of design patterns as blueprints — not exact code but concepts that guide how to structure and connect classes and objects to solve specific problems effectively.

In simple terms:

“A design pattern is a tried and tested way to solve a common programming challenge.”

💡 Why Use Design Patterns?

Design patterns are widely used in object-oriented programming because they:

1. Improve Code Reusability – Patterns provide reusable solutions that can be adapted across multiple projects.

2. Enhance Maintainability – They make code easier to understand, extend, and modify.

3. Promote Best Practices – They encourage clean architecture and separation of concerns.

4. Facilitate Communication – When developers talk in terms of “Singleton”, “Observer”, or “Factory”, they instantly understand the architecture idea.

5. Reduce Code Complexity – They help organize large codebases into manageable structures.

In short, design patterns help write better, cleaner, and scalable code.

🧩 Types of Design Patterns

Design patterns are categorized into three main types:

1. Creational Design Patterns

These patterns deal with object creation mechanisms, trying to create objects in a way that is suitable for the situation.
They abstract the instantiation process — making it more flexible and reusable.

Common Creational Patterns:

• Singleton → Ensures only one instance of a class exists.

• Factory Method → Creates objects without exposing the creation logic to the client.

• Abstract Factory → Provides an interface for creating families of related objects.

• Builder → Separates object construction from its representation.

• Prototype → Creates new objects by cloning existing ones.

2. Structural Design Patterns

These patterns focus on class and object composition — how objects are combined to form larger structures.
They help ensure that if one part of the system changes, the entire structure doesn’t need to change.

Common Structural Patterns:

• Adapter → Bridges between two incompatible interfaces.

• Decorator → Adds new functionality to an object dynamically.

• Facade → Provides a simplified interface to a complex subsystem.

• Composite → Treats individual objects and compositions uniformly.

• Proxy → Controls access to another object. 

3. Behavioral Design Patterns

These patterns are concerned with communication between objects — how they interact and share responsibilities.

Common Behavioral Patterns:

• Observer → Defines a one-to-many relationship between objects so that when one changes, others are notified.

• Strategy → Defines a family of algorithms, encapsulates each one, and makes them interchangeable.

• Command → Encapsulates a request as an object, allowing parameterization of clients.

• Iterator → Provides a way to access elements sequentially without exposing internal details.

• Mediator → Reduces coupling between communicating objects.