2 Advanced Class Design

[2.1 Identify when and how to apply abstract classes] (#)
[2.2 Construct abstract Java classes and subclasses] (#)
[2.3 Use the static and final keywords] (https://github.com/wevertonsreis/Java-SE-7-Programmer-II/wiki/2.3-Use-the-static-and-final-keywords)
[2.4 Create top-level and nested classes] (https://github.com/wevertonsreis/Java-SE-7-Programmer-II/wiki/2.4-Create-top-level-and-nested-classes)
[2.5 Use enumerated types] (https://github.com/wevertonsreis/Java-SE-7-Programmer-II/wiki/2.5-Use-enumerated-types)