Java Cookbook, 2nd Edition

Chapter 8. Data Structuring with Generics, foreach, and Enumerations (JDK 1.5)

Introduction

JDK 1.5 introduced two new concepts, Generics and AutoBoxing/Unboxing, and two new language features, “foreach” and typesafe enumerations; these features are covered in this chapter.

Generics allow a class to be tailored for a variety of argument/return types at compile time. It provides similar functionality to the Templates mechanism that has been in C++ for some years. When used with the Collections classes (see Chapter 7), Generics significantly increase type safety and remove the requirement for downcasting every object that is retrieved from a Collection (either directly or via an Iterator).

Recipe 5.3 discussed the “Wrapper” classes; these classes provide Objects that represent primitive values. Autoboxing automates the conversion from primitive to Object and vice versa.

The new "foreach” mechanism does not give Java a new keyword; the “for” keyword is still used. However, the syntax is changed slightly to resemble the “for value in list” construct in languages such as the Unix Bourne Shell and the Awk scripting language. This makes it much easier to use Collections, often eliminating the need to obtain an Iterator.

Finally, the Typesafe Enumerations feature provides a mechanism for dealing with a small list of discrete values, such as months, colors, and the like. It combines the enum syntax from Java’s predecessor, C, with the Typesafe Enumeration design pattern, giving JDK 1.5 ...