The most commonly used design pattern varies by application and developer preference. However, the “Singleton” pattern — which ensures that a class has only one instance and provides a global point of access to it — is frequently considered one of the most widely utilized design patterns in software development.
Table of Contents
The 7 most important software design patterns
9 mins read
Jun 15, 2026
Share
Design Patterns can be incredibly useful if used in the right situations and for the right reasons. They can make a programmer significantly more efficient by allowing them to avoid resolving common problems. They also provide a useful common language to conceptualize repeated problems and solutions when discussing with others or managing code in larger teams.
Design Patterns have become an object of some controversy in the programming world in recent times, largely due to their perceived overuse. Code with too many different design patterns is difficult to read or debug.
The best way to avoid problems with design patterns is to learn how and why to use each pattern.
Master dozens of the best design patterns.
Learn a design pattern to solve every situation and interview question.
Software Design Patterns: Best Practices for Software Developers
Singleton#
The singleton pattern is used to limit creation of a class to only one object. This is beneficial when one (and only one) object is needed to coordinate actions across the system. There are several examples of where only a single instance of a class should exist, including caches, thread pools, and registries.
It’s trivial to initiate an object of a class — but how do we ensure that only one object ever gets created? The answer is to make the constructor ‘private’ to the class we intend to define as a singleton. That way, only the members of the class can access the private constructor and no one else.
Important consideration: It’s possible to subclass a singleton by making the constructor protected instead of private. This might be suitable under some circumstances. One approach taken in these scenarios is to create a register of singletons of the subclasses and the getInstance method can take in a parameter or use an environment variable to return the desired singleton. The registry then maintains a mapping of string names to singleton objects, which can be accessed as needed.
Factory Method#
A normal factory produces goods; a software factory produces objects. And not just that — it does so without specifying the exact class of the object to be created.
To accomplish this, objects are created by calling a factory method instead of calling a constructor.
Usually, object creation in Java takes place like so:
`SomeClass someClassObject = new SomeClass();`
The problem with the above approach is that the code using the SomeClass’s object, suddenly now becomes dependent on the concrete implementation of SomeClass.
There’s nothing wrong with using new to create objects but it comes with the baggage of tightly coupling our code to the concrete implementation class, which can occasionally be problematic.
Strategy#
The strategy pattern allows grouping related algorithms under an abstraction, which allows switching out one algorithm or policy for another without modifying the client.
Instead of directly implementing a single algorithm, the code receives runtime instructions specifying which of the group of algorithms to run.
Observer#
This pattern is a one-to-many dependency between objects so that when one object changes state, all its dependents are notified. This is typically done by calling one of their methods.
For the sake of simplicity, think about what happens when you follow someone on Twitter. You are essentially asking Twitter to send you (the observer) tweet updates of the person (the subject) you followed. The pattern consists of two actors, the observer who is interested in the updates and the subject who generates the updates.
A subject can have many observers and is a one to many relationship. However, an observer is free to subscribe to updates from other subjects too. You can subscribe to news feed from a Facebook page, which would be the subject and whenever the page has a new post, the subscriber would see the new post.
Key consideration: In case of many subjects and few observers, if each subject stores its observers separately, it’ll increase the storage costs as some subjects will be storing the same observer multiple times.
Builder#
As the name implies, a builder pattern is used to build objects. Sometimes, the objects we create can be complex, made up of several sub-objects or require an elaborate construction process. The exercise of creating complex types can be simplified by using the builder pattern. A composite or an aggregate object is what a builder generally builds.
Key consideration: The builder pattern might seem similar to the ‘abstract factory’ pattern but one difference is that the builder pattern creates an object step by step whereas the abstract factory pattern returns the object in one go.
Adapter#
This allows incompatible classes to work together by converting the interface of one class into another. Think of it as a sort of translator: when two heads of states who don’t speak a common language meet, usually an interpreter sits between the two and translates the conversation, thus enabling communication.
If you have two applications, with one spitting out output as XML with the other requiring JSON input, then you’ll need an adapter between the two to make them work seamlessly.
State#
The state pattern encapsulates the various states a machine can be in, and allows an object to alter its behavior when its internal state changes. The machine or the context, as it is called in pattern-speak, can have actions taken on it that propel it into different states.
Without the use of the pattern, the code becomes inflexible and littered with if-else conditionals.
Software design patterns in action: Building a food delivery application#
Design patterns are often taught as individual concepts: Singleton manages a single instance, Factory Method creates objects, Strategy changes behavior, and so on. While these definitions are useful, they can make patterns feel disconnected from real software development.
In practice, modern applications rarely use just one pattern. Instead, multiple patterns work together to solve different architectural problems across the same system. Understanding how they fit together is often more valuable than memorizing their textbook definitions.
To see how this works, let's examine a food delivery platform similar to Uber Eats, DoorDash, or Foodpanda. This application supports user accounts, restaurant listings, order processing, payments, delivery tracking, and notifications. Along the way, it uses several design patterns to keep the system maintainable, flexible, and scalable.
Project overview#
Imagine a customer opening the application to order dinner. They browse restaurants, customize items, place an order, choose a payment method, and receive updates as the order moves through the delivery process.
Behind the scenes, multiple software components coordinate to make this experience possible:
User account management
Restaurant and menu services
Order processing
Payment handling
Delivery management
Notifications
Third-party integrations
Rather than solving every problem with custom code, architects use proven design patterns to address recurring challenges.
Singleton: Managing application configuration#
Every large application needs centralized configuration information.
The food delivery platform must store settings such as:
Database connection details
Payment gateway credentials
API keys
Feature flags
Environment-specific settings
A Singleton configuration manager ensures the entire application references a single source of truth.
ConfigurationManager├── Database Settings├── Payment Keys├── Feature Flags└── Environment Variables
Without a Singleton, different parts of the application could accidentally load different configurations, leading to inconsistent behavior. By maintaining a single shared instance, every component accesses the same settings throughout the application's lifecycle.
Factory Method: Creating payment processors#
Customers expect flexibility when paying for orders.
Some users prefer:
Credit cards
PayPal
Apple Pay
Google Pay
The checkout system shouldn't need to know the implementation details of every payment provider.
Instead, a Factory Method creates the appropriate processor:
PaymentFactory│├── CreditCardProcessor├── PayPalProcessor├── ApplePayProcessor└── GooglePayProcessor
When a customer selects a payment option, the factory returns the correct processor object. This keeps the checkout workflow loosely coupled and makes it easy to add new payment methods later.
Strategy: Calculating delivery fees#
Delivery pricing often changes based on business rules.
The platform may support:
Standard delivery
Express delivery
Peak-hour pricing
Promotional discounts
Rather than embedding all pricing logic inside one large method, the application uses the Strategy pattern.
DeliveryStrategy│├── StandardPricing├── ExpressPricing├── PeakHourPricing└── DiscountPricing
The checkout service selects the appropriate pricing strategy at runtime. This makes it easy to introduce new pricing models without modifying the rest of the application.
Observer: Sending notifications#
Order tracking is one of the most important features of a food delivery platform.
Whenever an order changes status, multiple stakeholders need updates:
The customer wants progress notifications.
The restaurant needs preparation updates.
The delivery driver needs pickup instructions.
This is a perfect use case for the Observer pattern.
Order Status Updated│▼Order Object│┌──────┼──────┐▼ ▼ ▼Customer Restaurant DriverObserver Observer Observer
When an order status changes, all registered observers automatically receive notifications. The order system doesn't need to know how each notification is delivered—it simply broadcasts the event.
Builder: Constructing complex orders#
Food orders can become surprisingly complex.
A single order may include:
Multiple menu items
Size selections
Toppings and customizations
Delivery instructions
Coupons and promotions
Creating an order through a large constructor quickly becomes difficult to maintain.
The Builder pattern simplifies object creation:
OrderBuilder.addBurger().addFries().addDrink().applyCoupon().addInstructions().build()
This approach improves readability and makes it easier to create complex order objects while ensuring all required fields are configured correctly.
Adapter: Integrating third-party services#
Most food delivery platforms rely on external services.
Examples include:
Payment providers
Mapping APIs
Delivery partners
SMS providers
The challenge is that each service exposes a different API.
The Adapter pattern creates a consistent interface:
Application│▼MapServiceAdapter│┌────┴────┐▼ ▼Google MapboxMaps API API
The rest of the application interacts with a standard interface while the adapter handles provider-specific details. This reduces coupling and makes future vendor changes much easier.
State: Managing order lifecycle#
Orders move through several stages before reaching the customer.
Placed↓Preparing↓Readyfor Pickup↓Outfor Delivery↓Delivered
Different actions are valid in different states.
For example:
A placed order can be canceled.
A delivered order cannot.
A preparing order can notify the restaurant.
An out-for-delivery order can share tracking updates.
The State pattern encapsulates these behaviors within individual state objects rather than relying on large conditional statements scattered throughout the codebase.
Architecture summary#
Pattern | Role in the application |
Singleton | Configuration management |
Factory Method | Payment processor creation |
Strategy | Delivery fee calculation |
Observer | Notifications |
Builder | Order creation |
Adapter | Third-party integrations |
State | Order status management |
What this example teaches#
This food delivery platform highlights an important reality of software architecture: design patterns rarely exist in isolation.
Each pattern solves a different engineering problem:
Singleton manages shared configuration.
Factory Method creates flexible object hierarchies.
Strategy enables interchangeable business rules.
Observer handles event-driven communication.
Builder simplifies complex object creation.
Adapter integrates external systems.
State manages changing behavior over time.
Together, these patterns make the application easier to extend, test, and maintain.
Just as importantly, they demonstrate that patterns should be introduced to solve actual problems. Adding patterns without a clear purpose often increases complexity rather than reducing it.
Final takeaway#
The most effective software architects don't memorize design patterns as isolated interview topics. They understand the problems each pattern was designed to solve and recognize when those problems appear in real systems.
A modern application such as a food delivery platform may use multiple patterns simultaneously because software systems face multiple architectural challenges at the same time. The goal isn't to use as many patterns as possible—it's to choose the right pattern when it improves maintainability, flexibility, or scalability.
When viewed through that lens, design patterns become less about theory and more about practical engineering decisions that help teams build better software.
What to learn next?#
Congratulations on learning these important 7 design patterns. However, there are many more to master.
To help you learn master all the most important design patterns, Educative has created Software Design Patterns: Best Practices for Software Developers.
The course is based on the popular book by the Gang of Four, but presented in an interactive, easy-to-digest format. You will master the 23 famous design patterns from the book interactively, learn the proper applications of the 3 key design pattern types (creational, structural, and behavioral), and learn to incorporate these design patterns into your own projects.
By the end of the course, you’ll have no problem designing and solving recurring software problems in interview or in practice.
Continue learning about design patterns#
Frequently Asked Questions
What is the most commonly used design pattern?
What is the most commonly used design pattern?
Written By:
Educative
Related Courses
Software Design Patterns: Best Practices for Software DevelopersSoftware Design Patterns in CDatabase Design Fundamentals for Software EngineersSoftware Architecture in Java: Design & DevelopmentMaster Software Design Patterns and Architecture in C++Clean Code in PythonBecome an Effective Software Engineering ManagerGrokking the Fundamentals of System DesignGrokking Modern System Design InterviewGrokking the Low Level Design Interview Using OOD PrinciplesSystem Design Deep Dive: Real-World Distributed SystemsKotlin Design Patterns and Best PracticesGrokking the Mobile System Design InterviewSystem Design Interview: Fast-Track in 48 HoursGrokking the Product Architecture Interview
