Design Patterns

Overview

Every software system eventually encounters similar design challenges. Objects become difficult to create, components become tightly coupled, integrations become complex, and functionality becomes difficult to extend.

Experienced engineers rarely invent solutions from scratch every time a problem appears.

Instead, they often rely on proven patterns that have consistently solved similar problems across many systems.

Design patterns are not frameworks, libraries, or rules.

They are reusable approaches that help solve frequently occurring design challenges.

A Running Example

Throughout this page, we will use a healthcare diagnostics platform as a running example.

As the platform evolves, engineers encounter common design challenges.

Design patterns help address these recurring challenges in a structured and proven way.

Why Design Patterns Matter

Software systems evolve continuously.

Requirements change, implementations grow, integrations expand, and teams scale.

Patterns help engineers build systems that are easier to modify and maintain over time.

Challenge	How Patterns Help
Growing Complexity	Provide Structure
Changing Requirements	Improve Flexibility
Testing Difficulties	Reduce Coupling
Maintenance Costs	Encourage Consistency
System Evolution	Support Extensibility

Patterns are valuable because software rarely remains static.

Understanding Design Patterns

A design pattern is best viewed as a reusable solution template rather than a specific implementation.

Every pattern addresses:

• A Repeating Problem
• A Proven Solution Approach
• Known Benefits
• Known Tradeoffs

Patterns help engineers communicate design ideas efficiently.

When someone suggests using a Strategy Pattern or Factory Pattern, experienced engineers immediately understand the type of problem being solved.

When Patterns Help

Patterns become valuable when similar design problems appear repeatedly.

Common signals include:

• Object Creation Logic Keeps Growing
• Large Conditional Statements Continue Expanding
• Multiple Implementations Exist
• Systems Require Greater Flexibility
• Components Need Better Separation

For example:

This is often a signal that a creation or behavioral pattern may be beneficial.

When Patterns Hurt

Patterns introduce abstractions, and every abstraction has a cost.

One of the most common mistakes is applying patterns before they are truly needed.

Pattern For Pattern’s Sake

Using a pattern simply because it exists often increases complexity without delivering meaningful benefits.

Premature Abstraction

Creating elaborate extension points before actual requirements exist frequently leads to unnecessary maintenance overhead.

Interface For Everything

Introducing interfaces when only a single implementation exists can create complexity that delivers little value.

Over-Engineering

A simple solution is often better than an elegant pattern applied to a trivial problem.

Pattern Categories

Design patterns are commonly grouped based on the type of problem they solve.

Creational Patterns

Focus on object creation.

Examples:

• Factory Pattern
• Builder Pattern

Structural Patterns

Focus on organizing and composing components.

Examples:

• Adapter Pattern
• Facade Pattern
• Decorator Pattern
• Proxy Pattern

Behavioral Patterns

Focus on interactions and behavior.

• Strategy Pattern
• Observer Pattern

The purpose of these categories is organization, not memorization.

Factory Pattern

The Factory Pattern is useful when object creation becomes complex or when multiple implementations may exist.

Instead of creating objects directly, creation logic is centralized.

In the diagnostics platform, notifications may be delivered through different channels.

Rather than scattering creation logic throughout the application, a factory determines which implementation should be created.

Benefits:

• Centralized Creation Logic
• Improved Flexibility
• Easier Extension

Avoid When:

• Only One Implementation Exists
• Creation Logic Is Trivial

Builder Pattern

The Builder Pattern helps construct complex objects step-by-step.

It is particularly useful when object creation involves many optional properties or multiple configuration combinations.

Consider creating a diagnostic order.

Without a builder, constructors often become difficult to understand and maintain.

Benefits:

• Improved Readability
• Flexible Object Construction
• Reduced Constructor Complexity

Avoid When:

• Objects Are Simple
• Few Parameters Exist

Strategy Pattern

The Strategy Pattern enables behavior to vary without modifying the consuming component.

A common indicator is large conditional logic controlling behavior.

Consider billing calculations.

Each billing approach may use different rules.

Benefits:

• Behavioral Flexibility
• Reduced Conditional Logic
• Improved Maintainability

Avoid When:

• Only One Behavior Exists
• Rules Rarely Change

Observer Pattern

The Observer Pattern allows multiple components to react when an event occurs.

This pattern appears frequently in event-driven architectures.

Consider a new diagnostic order being created.

Observers reduce direct dependencies between components.

Benefits:

• Loose Coupling
• Extensibility
• Event-Driven Workflows

Avoid When:

• Only One Consumer Exists
• Relationships Are Simple

Adapter Pattern

The Adapter Pattern helps integrate systems with incompatible interfaces.

This is extremely common in enterprise environments.

Imagine integrating multiple laboratory vendors.

Each vendor may expose different formats.

Benefits:

• Integration Flexibility
• Reduced Vendor Coupling
• Simplified Internal Design

Avoid When:

• Interfaces Already Match
• Additional Layer Adds No Value

Facade Pattern

The Facade Pattern provides a simplified interface to a complex subsystem.

Users interact with a single entry point rather than many internal components.

Consider patient information retrieval.

Instead of exposing all services directly, a facade can provide a simplified experience.

Benefits:

• Simplified Consumption
• Reduced Coupling
• Improved Maintainability

Avoid When:

• No Significant Complexity Exists
• Consumers Need Direct Control

Decorator Pattern

The Decorator Pattern adds behavior without modifying existing implementations.

It is particularly useful for cross-cutting concerns.

For example:

Benefits:

• Extension Without Modification
• Improved Flexibility
• Better Separation Of Concerns

Avoid When:

• Behavior Never Changes
• Simplicity Is More Important

Proxy Pattern

The Proxy Pattern controls access to another component.

It is frequently used for security, caching, and remote communication.

Examples include:

• Authorization Checks
• Caching Layers
• Remote Service Access
• Rate Limiting Controls

Benefits:

• Access Control
• Resource Protection
• Additional Operational Controls

Avoid When:

• No Additional Control Is Needed
• Added Indirection Creates Unnecessary Complexity

Dependency Injection

Dependency Injection reduces coupling by providing dependencies externally rather than creating them internally.

This improves:

• Testability
• Flexibility
• Maintainability

Dependency Injection is one of the most widely used design techniques in modern applications.

Common Pattern Combinations

Real-world systems rarely use a single design pattern in isolation.

As systems grow, multiple patterns often work together to solve larger design challenges.

Factory + Strategy

Common when behavior varies and must be selected dynamically.

Observer + Messaging

Frequently used in event-driven architectures.

Facade + Adapter

Very common in enterprise integration environments.

Decorator + Proxy

Common in security and operational monitoring scenarios.

Understanding pattern combinations is often more valuable than understanding individual patterns in isolation.

Choosing The Right Pattern

One of the most common mistakes is choosing a pattern before fully understanding the problem.

A practical approach is starting with the problem and then selecting an appropriate solution.

Problem	Pattern To Consider
Flexible Object Creation	Factory
Complex Construction	Builder
Changing Behavior	Strategy
Event Reactions	Observer
System Integration	Adapter
Simplifying Complexity	Facade
Extending Functionality	Decorator
Controlling Access	Proxy

Patterns should emerge naturally from requirements rather than being imposed on a design.

Real-World Case Study

Consider the healthcare diagnostics platform processing thousands of diagnostic orders every day.

Several patterns work together.

Each pattern solves a different problem.

Pattern	Responsibility
Observer	Event Notification
Factory	Object Creation
Strategy	Behavior Selection
Decorator	Additional Functionality
Proxy	Access Control

This example demonstrates how patterns often collaborate to support real-world business requirements.

Design Pattern Review Checklist

The following checklist can be used during design reviews and architecture discussions.

Patterns should create clarity rather than complexity.

Design Pattern Canvas

The Design Pattern Canvas helps evaluate whether a pattern should be introduced into a solution.

Area	Example
Problem	Multiple Notification Types
Pattern	Factory
Reason For Selection	Flexible Object Creation
Benefits	Simplified Extension
Tradeoffs	Additional Abstraction
Alternative	Direct Construction
Complexity Impact	Moderate
Future Flexibility	High

Common Anti-Patterns

Pattern Fever

Using patterns simply because they exist rather than because they solve a meaningful problem.

Factory Of Factory Of Factory

Excessive abstraction often creates confusion without providing measurable benefits.

Interface For Everything

Not every class requires an interface.

Premature Abstraction

Future requirements are often less certain than teams expect.

God Objects

One object accumulates too many responsibilities and becomes difficult to maintain.

Deep Inheritance Chains

Excessive inheritance often increases complexity and reduces flexibility.

Copy-Paste Design

Recurring problems are solved repeatedly rather than extracting reusable solutions.

How Patterns Connect

Patterns are part of a larger design ecosystem.

Patterns help implement principles such as:

• Separation Of Concerns
• Low Coupling
• High Cohesion
• Extensibility
• Maintainability

Over time, repeated use of patterns influences larger architectural structures and design decisions.

Key Takeaway