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6.8.1 Package Names

Names of packages that are to be made widely available should be formed
as described in ?7.7 . Such names are always qualified names whose first
identifier consists of two or three lowercase letters that name an
Internet domain, such as com, edu, gov, mil, net, org, or a two-letter
ISO country code such as uk or jp.

(http://java.sun.com/docs/books/jls/second_edition/html/names.doc.html#9184)

Packages in sun.* (not com.sun.*) are not guaranteed to exist. See
http://java.sun.com/products/jdk/faq/faq-sun-packages.html 

--- Vladimir

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Vladimir G. Ivanovic                        http://leonora.org/~vladimir
2770 Cowper St.                                         vladimir@xxxxxxx
Palo Alto, CA 94306-2447                                 +1 650 678 8014