Factory Method Design Pattern in Java (original) (raw)

The Factory Method Design Pattern is a Creational Design Pattern used to create objects without exposing the object creation logic to the client. It defines a method for creating objects, where subclasses decide which class object should be instantiated, making the application more flexible and maintainable.

• Encapsulates object creation logic from the client code
• Promotes loose coupling using interfaces or abstract classes
• Makes applications easier to extend with new object types
• Widely used in frameworks, libraries, and enterprise applications

• The client requests objects through the application class instead of creating them directly.
• The Factory Method creates and returns the required object such as Game, Banking, or Shopping.
• Object creation logic is hidden from the client, which works with interfaces or abstract classes instead of concrete objects, improving flexibility and reducing coupling.
• Since it deals with object creation, it belongs to the Creational Design Pattern category.

When to use Factory Method Design Pattern?

Factory method design pattern can be used in java in following cases:

• When a class cannot determine the type of objects it needs to create beforehand.
• When subclasses need to decide which objects should be created.
• When object creation logic should be delegated to helper subclasses while keeping the client code independent of concrete classes.

**Note: The client may still use new product types, but it interacts through a common abstraction, so major client-side changes are usually not required.

**Key Components of Factory Method Design Pattern

Below are the main components of Factory Method Design Pattern in Java:

1. Product

Defines a common interface or abstract class for all objects created by the factory.

interface Product {

void display();

}

2. Concrete Product

Implements the Product interface and defines specific behavior.

class ConcreteProductA implements Product {

public void display() {

System.out.println("Product A");

}

}

3. Creator

Declares the factory method that returns Product objects.

abstract class Creator {

abstract Product factoryMethod();

}

4. Concrete Creator

Implements the factory method and returns specific product objects.

class ConcreteCreatorA extends Creator {

Product factoryMethod() {

return new ConcreteProductA();

}

}

5. Factory Method

A method that creates and returns Product objects without exposing creation logic to the client.

Product p = new ConcreteCreatorA().factoryMethod();

Factory Method Design Pattern Example

We are developing an e-commerce system where different product categories (electronics, clothing, books) are created dynamically. You want to:

• Avoid tight coupling between client and object creation
• The client interacts with the common Product type, so adding new products usually requires extending factories rather than modifying client logic.
• Hide object creation logic

Solution using Abstract Class

Step 1: Abstract Product Class

Defines a common structure for all product types.

abstract class Product {

public abstract void display();

}

Step 2: Concrete Products

These are actual product implementations created by factory.

Java `

class ConcreteProductA extends Product { @Override public void display() { System.out.println("This is Concrete Product A."); } }

class ConcreteProductB extends Product { @Override public void display() { System.out.println("This is Concrete Product B."); } }

`

Step 3: Creator Abstract Class

Declares factory method but does not implement object creation.

abstract class Creator {

public abstract Product factoryMethod();

}

Step 4: Concrete Creators

Each class decides which product object to create.

Java `

class ConcreteCreatorA extends Creator { @Override public Product factoryMethod() { return new ConcreteProductA(); } }

class ConcreteCreatorB extends Creator { @Override public Product factoryMethod() { return new ConcreteProductB(); } }

`

Step 5: Client Code

Client uses factory to create objects without knowing actual classes.

Java `

public class FactoryMethodExample { public static void main(String[] args) {

    Creator creatorA = new ConcreteCreatorA();
    Product productA = creatorA.factoryMethod();
    productA.display();

    Creator creatorB = new ConcreteCreatorB();
    Product productB = creatorB.factoryMethod();
    productB.display();
}

}

`

Output

This is Concrete Product A. This is Concrete Product B.

**Explanation: In this approach, a Creator interface defines the factory method, and different factory implementations create specific products. It provides more flexibility since Java allows multiple interface implementations

Solution using Interface

Step 1: Product Interface

Defines contract for all product types.

interface Product {

void display();

}

Step 2: Concrete Products

Actual implementations of Product interface.

Java `

class ConcreteProductA implements Product { @Override public void display() { System.out.println("This is Concrete Product A."); } }

class ConcreteProductB implements Product { @Override public void display() { System.out.println("This is Concrete Product B."); } }

`

Step 3: Factory Interface

Defines factory contract for creating products.

interface Creator{

Product factoryMethod();

}

Step 4: Concrete Factories

Each factory creates specific product type.

Java `

class ConcreteCreatorA implements Creator{ @Override public Product factoryMethod() { return new ConcreteProductA(); } }

class ConcreteCreatorB implements Creator { @Override public Product factoryMethod() { return new ConcreteProductB(); } }

`

Step 5: Client Code

Client depends only on factory interface, not concrete classes.

Java `

public class FactoryMethodExample { public static void main(String[] args) {

    Creator creatorA = new ConcreteCreatorA();
    Product productA = creatorA.factoryMethod();
    productA.display();

    Creator creatorB = new ConcreteCreatorB();
    Product productB = creatorB.factoryMethod();
    productB.display();
}

}

`

Output

This is Concrete Product A. This is Concrete Product B.

**Explanation: In this approach, a Creator interface defines the factory method, and different factory implementations create specific products. It provides more flexibility since Java allows multiple interface implementations.

Features

• Separates object creation from client code
• Easy to add new product types because the client depends on interfaces or abstract classes, not concrete classes.
• Improves testability using mock objects
• Centralizes and reuses object creation logic
• Reduces dependency on concrete classes

Limitation

• Increases code complexity due to extra classes and interfaces
• Can lead to overengineering for simple object creation needs
• Adds slight runtime overhead due to polymorphism
• Makes system harder to understand for beginners
• Requires maintenance of both creator and product hierarchies

Simple Object Creation vs Factory Method