>>293 SwingWTっていうSwing/AWT互換ライブラリの例だけど
参考になると思う。

http://swingwt.sourceforge.net/faq.php
>Q. Couldn't you have used the java.awt.*/javax.swing.* package names? I have to search/replace all my code before I can use this stuff!
>A. Yes and No. Yes, technically it can be done, but it requires
> deployment to jre/lib/endorsed for javax.* packages (making it
> tougher to deploy apps). Other disadvantages are that the
> default Sun classloader will refuse to load anything starting
> with java.* (so you need to override the classloader), and the
> big worry that classes might get merged from the real AWT/Swing.
>
>You can also use various Java pre-processors or Ant to change your code at build time for you.

つーわけで、SwingWTではSunのJREと組み合わせて使うときには
置き換えをやらずに別のパッケージ名を使ってる。
gcjの場合はまた話が違うんだけど。