What are the differences between Factory, Factory Method, and Abstract Factory design patterns, and when should each be used?

Factory vs. Factory Method vs. Abstract Factory: Understanding the Differences

Understanding the differences between the Factory, Factory Method, and Abstract Factory design patterns can be challenging. To clarify, here's an explanation of each pattern and how they differ:

Factory

The Factory pattern creates objects without exposing the instantiation logic to the client. It refers to the newly created object through a common interface. In essence, it simplifies the Factory Method pattern.

Factory Method

The Factory Method defines an interface for creating objects, allowing subclasses to decide which class to instantiate. Similar to the Factory pattern, it uses a common interface to reference the created object.

Abstract Factory

The Abstract Factory pattern provides an interface for creating a family of related objects without specifying their concrete classes explicitly. This pattern is useful when you need to create multiple objects with a consistent interface.

Differences and When to Use

Pattern	Differences	When to Use
Factory	Simplified version of Factory Method	Use when you need a fixed, object-creation mechanism without subclassing.
Factory Method	Generic base class with specific creation logic handled by subclasses	Use when you need to vary the object type based on the subclass implementation.
Abstract Factory	Creates related objects of the same type	Use when you need to ensure consistency in creating object families for dependency injection or strategy patterns.

Java Examples

Factory:

<code class="java">public class FruitFactory {

  public Fruit makeFruit(String type) {
    switch (type) {
      case "Apple":
        return new Apple();
      case "Orange":
        return new Orange();
      default:
        throw new IllegalArgumentException("Invalid fruit type");
    }
  }
}</code>

Factory Method:

<code class="java">abstract class FruitPicker {

  protected abstract Fruit makeFruit();

  public void pickFruit() {
    Fruit fruit = makeFruit();
    // Perform operations using fruit...
  }
}

class ApplePicker extends FruitPicker {

  @Override
  protected Fruit makeFruit() {
    return new Apple();
  }
}

class OrangePicker extends FruitPicker {

  @Override
  protected Fruit makeFruit() {
    return new Orange();
  }
}</code>

Abstract Factory:

<code class="java">interface FruitPlantFactory {

  public Plant makePlant();
  public Picker makePicker();
}

class AppleFactory implements FruitPlantFactory {

  @Override
  public Apple makePlant() {
    return new Apple();
  }

  @Override
  public ApplePicker makePicker() {
    return new ApplePicker();
  }
}

class OrangeFactory implements FruitPlantFactory {

  @Override
  public Orange makePlant() {
    return new Orange();
  }

  @Override
  public OrangePicker makePicker() {
    return new OrangePicker();
  }
}</code>

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