The Factory Method pattern defines an interface for creating objects but allows subclasses to determine which object class to instantiate. This pattern encapsulates object creation and delegates it to subclasses, allowing classes to be extended without modifying the original code. The document also discusses why design patterns are useful, some strategies for using them like programming to interfaces, and themes and consequences of the Factory Method pattern like increased flexibility and eliminating hard-coded dependencies.

1. Factory Method Pattern Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.

2. Why Use Patterns Someone has already solved your problem Common terms facilitate communication The patterns emphasize the importance of context

3. Design Strategies recommended by GoF Design to Interfaces Favour composition over inheritance Find what varies and encapsulate it

4. Themes of Creational Patterns Encapsulate Knowledge about which concrete classes the system uses Hide how these classes are created and put together

5. Factory Method Pattern Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.

6. Applicability a class can't anticipate the class of objects it must create. a class wants its subclasses to specify the objects it creates. hiding which helper subclass has been delegated responsibility for implementing a task.

7. Factory Method Structure

8. Consequences Eliminates binding to a specific implementation at instance creation. Can increase sub-classing. Provides hooks for subclasses Connects parallel class hierarchies

9. Implementation With or without default implementation. Parameterized factory methods. Using templates to avoid sub-classing. Naming conventions.

10. Examples

11. Example 2