15 Nov 2011 sye   » (Journeyer)

From Philip Wadler's 'Java Generics and collections'


Part II provides a comprehensive introduction to the Collections Framework. Newton is reputed to have said, “If I have seen farther than others, it is because I stand on the shoulders of giants”. The best programmers live by this motto, building on existing frameworks and reusable code wherever appropriate. The Java Collections Framework provides reusable interfaces and implementations for a number of common collection types, including lists, sets, queues, and maps. There is also a framework for comparing values, which is useful in sorting or building ordered trees. (Of course, not all programmers exploit reuse. As Hamming said of computer scientists, “Instead of standing on each other’s shoulders, we stand on each other’s toes.”)

Thanks to generics, code using collections is easier to read and the compiler will catch more type errors. Further, collections provide excellent illustrations of the use of generics. One might say that generics and collections were made for each other, and, indeed, ease of use of collections was one of the main reasons for introducing generics in the first place.

Java 5 and 6 not only update the Collections Framework to exploit generics, but also enhance the framework in other ways, introducing interfaces and classes to support concurrency and the new enum types. We believe that these developments mark the beginning of a shift in programming style, with heavier use of the Collections Framework and, in particular, increased use of collections in favor of arrays. In Part II, we describe the entire framework from first principles in order to help you use collections more effectively, flagging the new features of Java 5 and 6 as we present them.

Following common terminology, we refer to the successive versions of Java as 1.0 up to 1.4 and then 5 and 6. We say ‘Java before generics’ to refer to Java 1.0 through 1.4, and ‘Java with generics’ to refer to Java 5 and 6.

The design of generics for Java is influenced by a number of previous proposals—notably, GJ, by Bracha, Odersky, Stoutamire, and Wadler; the addition of wildcards to GJ, proposed by Igarashi and Viroli; and further development of wildcards, by Torgersen, Hansen, Ernst, von der Ahé, Bracha, and Gafter. Design of generics was carried out under the Java Community Process by a team led by Bracha, and including Odersky, Thorup, and Wadler (as parts of JSR 14 and JSR 201). Odersky’s GJ compiler is the basis of Sun’s current javac compiler.


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