When to use Factory, Factory Method, and Abstract Factory Design Patterns?

Design Patterns: A Guide to Factory, Factory Method, and Abstract Factory

Introduction

The Factory family of design patterns provides a robust approach for managing object creation, concealing implementation details, and enhancing extensibility. This article explores the differences and appropriate usage of Factory, Factory Method, and Abstract Factory patterns.

Factory Pattern

The Factory pattern simplifies object creation by encapsulating instantiation logic within a dedicated class. This class serves as a centralized hub that produces objects without exposing the underlying implementation to the client code. Factory patterns refer to newly created objects through a common interface.

Factory Method Pattern

The Factory Method pattern goes a step further by defining an interface that determines which class to instantiate but leaves the actual instantiation to subclasses. This allows for greater flexibility and enables the creation of object hierarchies. Similar to the Factory pattern, Factory Method objects are referenced through a common interface.

Abstract Factory Pattern

The Abstract Factory pattern excels in creating families of related objects that share a common theme or functionality. This pattern defines an interface that provides methods for creating a range of related products. The client code interacts solely with the Abstract Factory, which ensures consistent object creation and enforces the family concept.

Distinguishing the Patterns

The key difference between these patterns lies in their level of extensibility and flexibility:

• Factory: Limited flexibility due to fixed implementation, but simple to use.
• Factory Method: Allows for subclassing and variation without the need for changing the client code.
• Abstract Factory: Provides the most flexibility, enabling the creation of object families with varying combinations and relationships.

When to Use Which Pattern

• Factory: Use when object creation is straightforward and does not require complex logic or extensibility.
• Factory Method: Consider when you need a generic base class that performs most of the object creation logic but allows for specialized subclasses to handle specific variations.
• Abstract Factory: Ideal for situations where you need to create a set of interconnected objects that adhere to a common structure and interface.

Example Implementations

• Factory:

  <code class="java">class FruitFactory {
    public static Apple createApple() { return new Apple(); }
    public static Orange createOrange() { return new Orange(); }
  }</code>

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• Factory Method:

  <code class="java">abstract class FruitPicker {
    protected abstract Fruit createFruit();
    public void pickFruit() { Fruit fruit = createFruit(); ... }
  }
  
  class ApplePicker extends FruitPicker {
    @Override
    protected Fruit createFruit() { return new Apple(); }
  }</code>

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• Abstract Factory:

  <code class="java">interface PlantFactory {
    Plant createPlant();
    Picker createPicker();
  }
  
  class AppleFactory implements PlantFactory {
    public Plant createPlant() { return new Apple(); }
    public Picker createPicker() { return new ApplePicker(); }
  }</code>

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