Thilan Dissanayaka Software Architecture February 02, 2020

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()).

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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.