Design Patterns in JDK Collections

Teaching Java is more challenging than teaching C++ or C, since instructors must at least survey various bundled and closely-related toolkits, beginning with the JDK API; for example, Swing, AWT, JDBC, JAXP, and the internationalization and collections frameworks, among others. Students of Java must learn when and how to leverage them; no one whose first instinct would be to implement a parser for some "little language" from scratch would find a job, let alone survive a first course in Java. Whatever sidebars introducing Design Patterns most texts offer are motivated by coverage of Swing, Java collections, or EJB. This is a tacit recognition that understanding design patterns is more critical to understanding these frameworks than, say, mechanics of the Java language. All these frameworks exemplify dependence on design patterns. Even a textbook such as Horstmann and Cornell1, although mentioning GOF patterns in connection with Java collections/Swing, merely scratches the surface, instead of structurally integrating them. The collections framework, in particular, offers a fairly well-defined and accessible domain within which design patterns enable achieving key architectural goals. Following the development of the collections framework through successive releases offers a case study on how design patterns interact with supporting graceful software evolution. At a tactical level, the collections framework provides a rich repository of decisions about how to implement design patterns, demonstrating how features of the Java language which may appear unmotivated when presented in textbook examples facilitate resolving implementation issues.