READING STILL IN PROGRESS

I may have been abit snobbish about Head First series in my review of Head First: Java, I take it back for this one. Design Patterns can be confusing, so the discussion style and image heavy approach to explaining helps.

The thing I like most about this is how the Design Patterns are alikened to real word implementations. So when looking at the Decorator Pattern it describes how Java's I/O Library makes heavy use of Decorators to help get a grip on the library and the Decorator pattern at the same time.

Here's some notes for myself on the different design patterns:

• Strategy - Composition over inheritance. Behaviours are defined in interfaces and the sub-classes implement the interface instead of directly inheriting from the parent class.
• Observer - When there's a publisher (or subject) that needs to trigger updates on various observers, instead of adding a function in the subject for each observer that should be abstracted out into a subject class that stores a list of observers and a method to subscribe or unsubscribe to these updates. This follows the Open/Closed Principle.
• Decorator -
• Factory Methods & Abstract Factories - Both intend to follow Dependency Inversion Principle. Factory Method does this using inheritance. Abstract Factory uses object composition and often includes a factory method. Factory Method relies on inherited subclass to define the composition