Design Patterns: Elements of Reusable Object-Oriented Software

Discussion of Behavioral Patterns

Chapter 5. Behavioral Patterns

Discussion of Structural Patterns

a class encapsulates state and operations, while a subsystem encapsulates classes.

Discussion of Creational Patterns

The creational patterns provide different ways to remove explicit references to concrete classes from code that needs to instantiate them:

How to Use a Design Pattern

How to Select a Design Pattern

when you eliminate dependencies on specific operations by isolating and encapsulating each operation, you make it easier to reuse an operation in different contexts

Object composition in general and delegation in particular provide flexible alternatives to inheritance for combining behavior. New functionality can be added to an application by composing existing objects in new ways rather than by defining new subclasses of existing classes. On the other hand, heavy use of object composition can make designs harder to understand. Many design patterns produce designs in which you can introduce customized functionality just by defining one subclass and composing its instances with existing ones