If yes, then you’ve probably faced this problem:

“Every time I add a new type of object, I need to change multiple places in the code. It becomes messy and tightly coupled.”

This is a common pain point in software design. The Factory Design Pattern is here to fix that.

// Step 1: Common Interface
public interface Notification {
    void send(String message);
}

// Step 2: Concrete Classes
public class EmailNotification implements Notification {
    public void send(String message) {
        System.out.println("Sending EMAIL: " + message);
    }
}

public class SMSNotification implements Notification {
    public void send(String message) {
        System.out.println("Sending SMS: " + message);
    }
}

public class PushNotification implements Notification {
    public void send(String message) {
        System.out.println("Sending PUSH: " + message);
    }
}

// Step 3: Factory Class
public class NotificationFactory {
    public static Notification createNotification(String type) {
        if (type == null || type.isEmpty()) return null;
        switch (type.toUpperCase()) {
            case "EMAIL": return new EmailNotification();
            case "SMS": return new SMSNotification();
            case "PUSH": return new PushNotification();
            default: throw new IllegalArgumentException("Unknown notification type " + type);
        }
    }
}

// Step 4: Client Code
public class Main {
    public static void main(String[] args) {
        Notification notification = NotificationFactory.createNotification("EMAIL");
        notification.send("Factory Pattern in Action!");
    }
}

🧠 What Just Happened?

Now, your Main or NotificationService doesn’t need to know how notifications are created — it just asks the factory for one.

If tomorrow you add WhatsAppNotification, you just update the factory, not every place in your app.

Important for the Spring Boot developer

💬 Your Question:

“If we’re using frameworks like Spring, then we don’t face the problem of using new everywhere. So, do we still need the Factory Pattern?”

Let’s unpack this clearly — because this is exactly where most developers get confused when learning design patterns in the age of frameworks like Spring Boot.

Spring itself already uses the Factory Pattern internally — that’s why you don’t have to use new.
But understanding the Factory Pattern is still essential — because Spring’s entire dependency injection system is built on top of it.

🧩 Without Spring — Manual Object Creation

When you don’t use Spring, you do something like this:

Notification notification = new EmailNotification();
notification.send("Hello!");

or

if (type.equals("SMS")) {
    notification = new SMSNotification();
}

👉 You’re manually creating objects with new.
If you add a new type tomorrow, you have to modify your code — it’s tightly coupled.

🏭 With Spring — Factory in Action (But Hidden)

When you use Spring:

@Service
public class NotificationService {
    @Autowired
    private Notification notification;
}

You never write new EmailNotification() — right?

That’s because the Spring Container (ApplicationContext) acts like a Super Factory:

• It creates objects for you (beans).

• It decides which implementation to inject.

• It manages their lifecycle (singleton, prototype, etc.).

Under the Hood

Spring uses:

• BeanFactory → The root factory that creates and manages beans.

• ApplicationContext → A more advanced factory that supports AOP, events, and message sources.

So yes — the Factory Pattern is at the core of Spring’s architecture.
You don’t see it, but it’s running behind every @Autowired.

🧠 Why You Should Still Learn the Factory Pattern

Even though Spring handles object creation for you, understanding the Factory Pattern helps you:

1. Understand Spring’s internals
   → You’ll know how BeanFactory, ApplicationContext, and dependency injection work.

2. Write cleaner custom factories
   → Sometimes, you still need to decide at runtime which object to create based on user input or configuration.
   Example: Payment gateway selector — Stripe, Razorpay, or PayPal.

    public interface PaymentGateway { void pay(); }
   
    public class StripeGateway implements PaymentGateway { public void pay() { ... } }
    public class RazorpayGateway implements PaymentGateway { public void pay() { ... } }
   
    @Component
    public class PaymentFactory {
        public PaymentGateway getGateway(String type) {
            return switch (type) {
                case "STRIPE" -> new StripeGateway();
                case "RAZORPAY" -> new RazorpayGateway();
                default -> throw new IllegalArgumentException("Unknown gateway: " + type);
            };
        }
    }
   

   You can still inject this factory into services, but the decision logic is yours.

3. Design framework-agnostic systems
   → In interviews or low-level architecture design, you may be asked to design without frameworks.
   Understanding the pattern helps you explain and design the logic yourself.

🏁 Final Thought

“If you find yourself changing the same class every time you add a new type of object — it’s time to use the Factory Pattern.”

The Factory Design Pattern helps you build clean, maintainable, and scalable systems by letting your code focus on behavior, not object creation.

You start with a simple class — maybe a User. It only needs a name and email.

Then the next feature arrives.

Now you need phone, address, gender, profile photo, preferences, and whatnot.

Before you realize it, your constructor looks like this 👇

User user = new User("Aditya", "aditya@gmail.com", "9876543210", "Male", "Bhopal",
 "image.png", true, false, LocalDate.now());

And the next developer who opens your class?
They’ll cry first, then quit. 😩

⚙️ The Problem: The Telescoping Constructor Nightmare

This is called the Telescoping Constructor Problem —
when your class grows with too many optional parameters, you end up with:

• Huge constructors

• Confusing parameter order

• Hard-to-read code

• Nightmare when adding new fields

🧩 The Need for a Better Way

We need a way to create objects like:

User user = new UserBuilder()
    .setName("Aditya")
    .setEmail("aditya@gmail.com")
    .setPhone("9876543210")
    .build();

Clean. Readable. Flexible.
That’s where the Builder Pattern comes in.

What Is the Builder Pattern?

The Builder Pattern is a creational design pattern that lets you construct complex objects step by step.
It separates object construction from its representation, allowing you to create different types or variations of objects using the same construction process.

In simple words:

Instead of passing 10 parameters into a constructor,
you “build” the object step-by-step using meaningful methods.

❌ Without Builder Pattern (Constructor Hell)

public class User {
    private String name;
    private String email;
    private String phone;
    private String address;

    public User(String name, String email, String phone, String address) {
        this.name = name;
        this.email = email;
        this.phone = phone;
        this.address = address;
    }
}

Creating a user:

User user = new User("Aditya", "aditya@gmail.com", "989654XXXX", "Bhopal");

Now imagine you add 4 more parameters later. You’ll end up with constructor overloads and confusion.

✅ With Builder Pattern

public class User {
    private String name;
    private String email;
    private String phone;
    private String address;

    private User(UserBuilder builder) {
        this.name = builder.name;
        this.email = builder.email;
        this.phone = builder.phone;
        this.address = builder.address;
    }

    public static class UserBuilder {
        private String name;
        private String email;
        private String phone;
        private String address;

        public UserBuilder setName(String name) {
            this.name = name;
            return this;
        }

        public UserBuilder setEmail(String email) {
            this.email = email;
            return this;
        }

        public UserBuilder setPhone(String phone) {
            this.phone = phone;
            return this;
        }

        public UserBuilder setAddress(String address) {
            this.address = address;
            return this;
        }

        public User build() {
            return new User(this);
        }
    }
}

Now creation looks like:

User user = new User.UserBuilder()
    .setName("Aditya Singh Rajput")
    .setEmail("aditya@gmail.com")
    .setPhone("9876543210")
    .setAddress("Bhopal")
    .build();

✅ Readable
✅ Flexible
✅ Easy to add new fields later

🏗️ Real-Life Use Case

Think about creating an Order or Product entity in an eCommerce system.
Some fields are mandatory, while others are optional (like discounts, coupons, etc.).

Using the Builder Pattern makes object creation clear, controlled, and scalable.
That’s why frameworks like Lombok’s , @Builder, Spring Boot DTOs, and even Java Streams internally follow similar principles.

you feel their need when your code becomes a tangled mess.
Let’s look at how one extra feature request can turn clean code into chaos — and how a pattern can save you.”

💭 Start with a Real Developer’s Struggle

Let’s take a very relatable example from my Java or Flutter experience.
Imagine this situation 👇

🧩 Scenario: The “Spaghetti Code” Factory Problem

You’re building an eCommerce app.
At first, you only support Card Payments.

So, you write:

if (paymentType.equals("CARD")) {
    processCardPayment();
}

All good ✅
But later, you add:

• UPI Payment

• Wallet Payment

• Cash on Delivery

Your code becomes:

if (paymentType.equals("CARD")) {
    processCardPayment();
} else if (paymentType.equals("UPI")) {
    processUPIPayment();
} else if (paymentType.equals("WALLET")) {
    processWalletPayment();
} else if (paymentType.equals("COD")) {
    processCODPayment();
}

Looks okay?
Wait till the next requirement hits you…

“We need to add Crypto payment next week, and refund feature later.”

Now every time a new payment method comes, you’ll:

• Modify this code again 😩

• Risk breaking something else 😩

• Have to test everything again 😩

This is code that grows horizontally (more if-else) — it violates the Open/Closed Principle.
Your code is open for modification when it should be open for extension.

🧠 And here comes the realization…

You pause and think:

“Why can’t I just have a flexible system that lets me add new payment methods without touching the core logic?”

That’s when you realize you need a Design Pattern.

⚙️ Solution: Factory Method Pattern

You apply a Factory Method Pattern, which creates payment objects dynamically:

interface Payment {
    void process();
}

class CardPayment implements Payment {
    public void process() { System.out.println("Processing Card Payment"); }
}

class UPIPayment implements Payment {
    public void process() { System.out.println("Processing UPI Payment"); }
}

class PaymentFactory {
    public static Payment getPayment(String type) {
        return switch (type) {
            case "CARD" -> new CardPayment();
            case "UPI" -> new UPIPayment();
            default -> throw new IllegalArgumentException("Invalid payment type");
        };
    }
}

Now your main logic becomes:

Payment payment = PaymentFactory.getPayment("CARD");
payment.process();

If you add a new payment method tomorrow (like Crypto),
you create a new class, not change old ones.

✅ Code is extensible
✅ Clean and maintainable
✅ No repeated conditionals

🔥 Another Realistic Example: The Singleton Problem

Scenario:

You’re building a logging system in a backend app.
You notice that multiple parts of your app are writing to logs —
but different parts create their own logger objects.

You end up with:

• Multiple log files,

• Duplicate messages,

• Messy output.

Then you realize —
you actually only need one logging instance shared across the entire app.

That’s when you use a Singleton pattern.

Don’t tightly couple your main code with details.
Both should depend on abstractions (like interfaces or abstract classes).“

Daily Life Example

Imagine:

• High-level module = TV Remote

• Low-level module = TV

Without Dependency Inversion:

Remote directly knows about SamsungTV and its buttons

• This means the Remote will only work with a Samsung TV.

• If you bring an LG TV, you’ll need to change the Remote code.

• This is tight coupling and bad design.

With Dependency Inversion:

• We create a TV interface that defines basic functions:

interface TV {
    void turnOn();
    void turnOff();
    void changeChannel(int ch);
}

• Now, SamsungTV and LGTV both implement this interface.

• Remote depends on the TV interface, not a specific TV.

class Remote {
    TV tv;  // depends on abstraction
    void pressPower() { tv.turnOn(); }
}

• Now the Remote can work with any TV.

• If you change the TV, Remote code does not need to change. ✅

Summary

• DIP means: "High-level code should not depend on low-level code. Work via abstractions."

• Real-life example: Remote depends on TV interface, not Samsung or LG TV.

• Benefit: Flexible, maintainable, easy to extend in the future.

👀 Real Life Example

Let’s imagine we are designing an app for different types of workers:

❌ Bad Example (Violating ISP)

public interface Worker {
    void work();
    void eat();
}

Now we have:

public class HumanWorker implements Worker {
    public void work() {
        System.out.println("Human working...");
    }

    public void eat() {
        System.out.println("Human eating...");
    }
}

public class RobotWorker implements Worker {
    public void work() {
        System.out.println("Robot working...");
    }

    public void eat() {
        // ❌ Robot doesn’t eat — but it’s forced to implement this
        throw new UnsupportedOperationException("Robot can't eat");
    }
}

👉 Here, the RobotWorker is forced to implement eat() even though it doesn’t make sense — violating Interface Segregation Principle.

✅ Good Example (Following ISP)

We break the interface into smaller, more specific ones:

public interface Workable {
    void work();
}

public interface Eatable {
    void eat();
}

Now we can do:

public class HumanWorker implements Workable, Eatable {
    public void work() {
        System.out.println("Human working...");
    }

    public void eat() {
        System.out.println("Human eating...");
    }
}

public class RobotWorker implements Workable {
    public void work() {
        System.out.println("Robot working...");
    }
}

✅ Each class now implements only what it needs.

⚙️ In Real-World Development

• This principle makes your code modular and flexible.

• It becomes easier to extend and maintain.

• Commonly used in Spring Boot, where services implement specific small interfaces rather than one huge one.

The Interface Segregation Principle (I in SOLID) is mostly used to solve problems related to “fat interfaces” — that is, when interfaces become too large and force classes to implement unnecessary methods.

Let’s break it down clearly 👇

⚠️ Main Issue It Solves

“Too many responsibilities or unnecessary methods in one interface.”

In short —
It solves tight coupling and unnecessary implementation problems between interfaces and classes.

💡 Real-Life Example

Think of this:

• You have a class Bird that can fly().

• You create a subclass Sparrow (it can fly ✅).

• Then you create another subclass Ostrich (it cannot fly ❌).

If your program expects all Birds to fly, using Ostrich will break your logic — which violates LSP.

So, Ostrich should not extend Bird if Bird assumes “can fly”.

// ❌ Violates LSP
class Bird {
    void fly() {
        System.out.println("Flying...");
    }
}

class Sparrow extends Bird {}  // OK
class Ostrich extends Bird {   // Problem
    @Override
    void fly() {
        throw new UnsupportedOperationException("Ostrich can't fly!");
    }
}

// ✅ Correct Approach
interface Bird {}
interface FlyingBird extends Bird {
    void fly();
}

class Sparrow implements FlyingBird {
    public void fly() {
        System.out.println("Flying...");
    }
}

class Ostrich implements Bird {
    // Ostrich doesn't fly, but still a bird — no LSP violation.
}

More Examples:-

🧾 1. Payment System Example (E-commerce App)

Imagine you have a PaymentService interface that processes payments.

You have classes like:

• CreditCardPayment

• PayPalPayment

• UPIPayment

Each one should behave like a payment service — if one fails to behave differently (e.g., throws error on same method), it violates LSP.

interface PaymentService {
    void pay(double amount);
}

class CreditCardPayment implements PaymentService {
    public void pay(double amount) {
        System.out.println("Paid " + amount + " using Credit Card");
    }
}

class PayPalPayment implements PaymentService {
    public void pay(double amount) {
        System.out.println("Paid " + amount + " using PayPal");
    }
}

// ❌ Violating LSP
class CashOnDeliveryPayment implements PaymentService {
    public void pay(double amount) {
        throw new UnsupportedOperationException("Cash payment not supported online!");
    }
}

Here, CashOnDeliveryPayment breaks LSP because it cannot be used wherever a PaymentService is expected.
It will crash the program.

✅ Fix: Don’t force it into the same inheritance; maybe separate interfaces:

interface OnlinePaymentService extends PaymentService {}
interface OfflinePaymentService {
    void collectCash();
}

📦 2. Inventory System Example

🔹 English:

Suppose your app has a base class InventoryItem.
You create child classes like:

• PerishableItem (milk, fruits)

• NonPerishableItem (phone, laptop)

If the parent class has a method like calculateExpiryDate(), and non-perishable items can’t have expiry, that’s an LSP violation.

✅ Fix → Move expiry logic to a subclass or new interface.

Nai aya samajh 🤔 ?

💡 Simple Meaning:

• You can add new behavior to the class

• But you should not change its existing code

Agaya samajh but Abhi clear nai hua example se dekhte hai…

🧍‍♂️ Real-Life Example:

Imagine you have a mobile phone.
Now, you want to:

• Add a new back cover

• Add a screen guard

You don't open the mobile’s internal parts, right?
You just add things on top of it → that’s extension without modification ✅

❌ Bad Java Example (Breaks OCP):

 public class PaymentService {
    public void makePayment(String paymentType) {
        if (paymentType.equals("creditcard")) {
            System.out.println("Paid with Credit Card");
        } else if (paymentType.equals("paypal")) {
            System.out.println("Paid with PayPal");
        }
    }
}

😵 Problem:

• Every time a new payment method comes (like UPI, Bitcoin), you have to edit this class.

➡️ Code is not closed for modification ❌

✅ Good Java Example (Follows OCP):

Step 1: Create an interface

public interface PaymentMethod {
    void pay();
}

Step 2: Implement different payment methods

public class CreditCardPayment implements PaymentMethod {
    public void pay() {
        System.out.println("Paid with Credit Card");
    }
}

public class PayPalPayment implements PaymentMethod {
    public void pay() {
        System.out.println("Paid with PayPal");
    }
}

Step 3: Use them without changing logic

public class PaymentService {
    public void makePayment(PaymentMethod method) {
        method.pay();  // No if-else, no changing code
    }
}

✅ Now, to add a new method like UPI:

public class UpiPayment implements PaymentMethod {
    public void pay() {
        System.out.println("Paid with UPI");
    }
}

No need to touch PaymentService — just extend the code with a new class 🚀.

💡 Hinglish Explanation:

Jab hum koi class banate hain, toh hum chahte hain ki:

• Naya feature add kar sakein (open for extension ✅)

• Purani code ko change na karna pade (closed for modification ✅)

Matlab:

• Jab naye requirement aaye, toh nayi class banao ya existing class ko extend karo

• Lekin purane code ko touch mat karo, warna bugs aa sakte hain

💡 Simple Explanation:

If one class handles too many things, any change in one part might accidentally break other parts. That’s risky and messy.

💻 Java Example (❌ Bad - Violates SRP):

public class Employee {
    public void calculateSalary() {
        // Logic to calculate salary
    }

    public void saveToDatabase() {
        // Logic to save employee data
    }

    public void generateReport() {
        // Logic to generate report
    }
}

❌ Here, the Employee class is doing too many things:

• Salary logic

• Database logic

• Report generation

✅ Good Code (Follows SRP):

public class Employee {
    private String name;
    private double salary;

    // Only employee-related properties
}

public class SalaryCalculator {
    public void calculateSalary(Employee employee) {
        // Logic to calculate salary
    }
}

public class EmployeeRepository {
    public void saveToDatabase(Employee employee) {
        // Logic to save employee data
    }
}

public class ReportGenerator {
    public void generateReport(Employee employee) {
        // Logic to generate report
    }
}

✅ Now, each class has one job:

• Employee → holds employee data

• SalaryCalculator → calculates salary

• EmployeeRepository → saves to database

• ReportGenerator → creates reports

✅ Trick to Check SRP (Hinglish for better understanding):

1. Class ka naam padhke socho:
   "Kya ye class sirf ek kaam ka representative lag rahi hai?"

2. Uske methods dekh ke socho:
   "Kya sabhi methods ek hi type ka kaam kar rahe hain?"

👉 Is class ko kab kab change karna padega?

• Business ne bola calculation logic change karo → calculateTotal()

• Printing format change hua → printInvoice()

• Database change hua → saveToDatabase()

➡️ Teen alag-alag reason se change karna pad raha hai. So, SRP break ho gaya.

🧠 Why use SOLID?

• Code becomes easy to understand

• Fewer bugs

• Easier to change and update

• Promotes reusability

🔠 Let’s break down SOLID one-by-one with daily life examples:

1. S - Single Responsibility Principle

One class should have only one job/responsibility.

🧠 Example: A Housemaid

• One maid for cooking

• Another for cleaning

• Another for washing clothes

If 1 maid does everything, it’s messy. Just like that, a class should only focus on one thing.

✅ So if something goes wrong in cooking, we don’t touch the cleaning part.

2. O - Open/Closed Principle

Software should be open for extension, but closed for modification.

🧠 Example: Mobile Phone Cases

• Your phone can add a new case (extend)

• But the phone’s internal structure stays the same (not modified)

✅ You should be able to add new features without changing old code.

3. L - Liskov Substitution Principle

Subclasses should be able to replace their parent classes without breaking anything.

🧠 Example: Charging Devices

• If you have a charger slot that fits a phone charger, it should also support any new phone model charger (as long as it’s a phone).

✅ Child class should behave properly when used in place of the parent class.

4. I - Interface Segregation Principle

Don’t force a class to implement things it doesn’t use.

🧠 Example: Remote Controls

• A TV remote has TV buttons

• A Fan remote doesn’t need volume buttons

❌ Don’t give a remote buttons it never uses
✅ Create small, separate interfaces for different jobs

5. D - Dependency Inversion Principle

Depend on abstractions, not on concrete classes.

🧠 Example: Electricity Plug

• You plug your phone, fridge, or washing machine into the same socket

• The socket doesn't care what device it is – it just gives power

✅ Your code should depend on general things (like interfaces) not specific ones (like exact classes)

✅ For Now…

We have learned what SOLID principles are all about and also saw some daily life examples to understand them in a simple way.

But still, things might not be fully clear, right?

Don’t worry!

To get complete clarity, we’ll now go one-by-one through each SOLID principle with a real Java code example so that you understand:

• What the principle means

• What happens if we break it

• How to follow it correctly in Java

👨‍💻 Who Am I?

I'm a Computer Science Engineering student from Sagar Institute of Science and Technology, Bhopal, and I’m deeply passionate about Java development, backend systems, and building real-world projects that make an impact.

Over the past 1.5 years, I've immersed myself in Java and Spring Boot, worked on exciting eCommerce backends, explored Flutter, and even implemented authentication systems like JWT and OAuth2. I'm always hungry to learn, build, and grow — and now, I’m stepping into the world of blogging to share that journey with you!

🧠 Why I Started Blogging?

To be honest, I've always believed in learning out loud. Whether it’s a bug I fixed after hours of struggle or a new concept I mastered, I feel there's always something worth sharing. So here’s why I started this blog:

• ✅ To document my learning journey 📚

• ✅ To help others avoid the roadblocks I faced 🚧

• ✅ To grow as a developer by writing and reflecting 💡

• ✅ To connect with like-minded folks from the dev community 🤝

💡 What Can You Expect From This Blog?

I'll be sharing:

• My learnings in Java, Spring Boot, and backend architectures

• Projects I'm building — including code, architecture decisions, and challenges

• Guides on topics like JWT Auth, OAuth2 login, and API design

• My journey learning React, Flutter, and mastering DSA

• Insights from internships, coding routines, productivity tips, and more!

Whether you're a beginner developer, a student like me, or someone curious about tech, I hope you’ll find something valuable here.

🌱 Let's Learn and Grow Together

Blogging is new to me, and I’m excited (and a little nervous) to be honest 😅 — but I know this is going to be a rewarding journey.

If you're reading this, thank you so much for being here. Your support means the world to me. 🙌

Let’s connect, learn, and grow — one blog at a time. 🚀
If you have any thoughts, suggestions, or just want to say hi, drop a comment below! 💬

See you in the next post! 😊

— Aditya Singh Rajput