Thilan Dissanayaka Design Patterns Apr 26

Factory Pattern explained simply

Factory Pattern

Imagine you want to create objects — but you don't want to expose the creation logic to the client and instead ask a factory class to create objects for you.

That's exactly what the Factory Pattern does.

What is the Factory Pattern?

At its core:

  • Defines an interface for creating an object.
  • Lets subclasses alter the type of objects that will be created.
  • Centralizes object creation, making code more flexible and easier to maintain.

Real-Life Analogy

Think about a bakery:

  • You place an order for a "cake".
  • You don't worry about how it’s baked.
  • The bakery (factory) prepares and gives you the cake.

You simply ask for an object and get it.

Structure

  • Product: Common interface for all objects the factory creates.
  • Concrete Products: Different implementations of the product interface.
  • Creator (Factory): Contains a method that returns objects of the Product type.

Simple Java Example

First, define a Shape interface:

public interface Shape {
    void draw();
}

Concrete implementations:

public class Circle implements Shape {
    @Override
    public void draw() {
        System.out.println("Drawing a Circle");
    }
}

public class Square implements Shape {
    @Override
    public void draw() {
        System.out.println("Drawing a Square");
    }
}

public class Rectangle implements Shape {
    @Override
    public void draw() {
        System.out.println("Drawing a Rectangle");
    }
}

Create the ShapeFactory:

public class ShapeFactory {
    // Factory method
    public Shape getShape(String shapeType) {
        if (shapeType == null) {
            return null;
        }

        if (shapeType.equalsIgnoreCase("CIRCLE")) {
            return new Circle();
        } else if (shapeType.equalsIgnoreCase("SQUARE")) {
            return new Square();
        } else if (shapeType.equalsIgnoreCase("RECTANGLE")) {
            return new Rectangle();
        }

        return null;
    }
}

Using the Factory

public class MainProgram {
    public static void main(String[] args) {
        ShapeFactory shapeFactory = new ShapeFactory();

        Shape shape1 = shapeFactory.getShape("CIRCLE");
        shape1.draw();

        Shape shape2 = shapeFactory.getShape("SQUARE");
        shape2.draw();

        Shape shape3 = shapeFactory.getShape("RECTANGLE");
        shape3.draw();
    }
}

Output:

Drawing a Circle
Drawing a Square
Drawing a Rectangle

Why Use the Factory Pattern?

  • Encapsulates object creation: Changes to object creation code are centralized.
  • Decouples code: Client code depends on abstractions, not concrete classes.
  • Easier maintenance and scalability: Add new product types without changing existing client code.

Real-World Use Cases

  • GUI Toolkits: Creating buttons, windows, menus.
  • Java Libraries: Calendar.getInstance(), NumberFormat.getInstance().
  • Database Drivers: Connection creation (DriverManager.getConnection()).

Factory Pattern vs. Abstract Factory Pattern

  • Factory Pattern: Creates one product type.
  • Abstract Factory Pattern: Creates families of related products.

Summary

The Factory Pattern helps you delegate object creation to a separate method or class.
It hides the instantiation details and allows your code to depend on interfaces rather than concrete classes — making it more flexible, robust, and easier to extend.

ALSO READ
SQL injection login bypass
Apr 26 Web App Hacking

SQL Injection (SQLi) is one of the oldest and most fundamental web application vulnerabilities. While it’s becoming rarer in modern web apps due to better coding practices and frameworks,....

Database Indexing: Speeding Up Your Queries Like a Pro
Apr 26 Database Systems

In the world of databases, speed matters. Whether you're powering an e-commerce store, a social media app, or a business dashboard — users expect data to load instantly. That’s where database....

Observer Pattern explained simply
Apr 26 Design Patterns

When one object needs to notify many other objects about changes in its state **automatically**, the **Observer Pattern** steps in. ## What is the Observer Pattern? - Defines a....

Adapter Pattern explained simply
Apr 26 Design Patterns

Ever needed to connect two incompatible interfaces without changing their source code? That’s exactly where the **Adapter Pattern** shines! The Adapter Pattern is a structural design pattern....

How stack works in function call
Mar 23 Web App Hacking

## The Stack in Computer Science The stack is an important concept in computer science. If you are planning to learn reverse engineering, malware analyzing, exploitation, etc., this concept is a....

Tic-Tac-Toe Game with Atmega 256 MicroController
Mar 23 Software Architecture

In this blog, I’ll walk you through how I built a **Tic-Tac-Toe game** using an AVR microcontroller, a 4x3 keypad, and a grid of LEDs. This project combines the basics of embedded programming, game....