Question

I am learning more about the factory design pattern and came across the following example from Microsoft (I recoded it in java). Example here

Short version:

• An abstract Product class

• A Concrete Product class that extends Product

• An abstract Factory class

• A Concrete Factory class that extends Factory

• An Assembly class

  public class ProductAssembler {
  
  public void AssembleProduct(Factory factory)
  {
  Product p = factory.getProduct();
  //do something
  }
  }
  

• A client

  public static void main(String[] args)
  {
  Factory factory = new ConcreteFactory();
  new ProductAssembler().AssembleProduct(factory);
  }
  

Question:

• What is the purpose of creating a factory object in the main method instead of a product object, why don’t they pass a product object to the assembleproduct method and change
  that method so it accepts products instead of factories?
• Is the assembly class also part of the ‘client’ or not?

Thanks

Answer 1

assembleProduct() in ProductAssembler doesn’t want to deal with instantiating products. So it wants to delegate this to a Factory so that when newer kinds of products are introduced, the existing factory changes (or a new factory is added) but ProductAssembler doesn’t need to change. Instead of instantiation, assembleProduct() calls factory.getProduct().

As far as the Factory pattern is concerned, ProductAssembler is the client. But if you look at it from an application perspective, your main() is the client and hence doesn’t deal with Product objects.