/usr/jdk или /usr/lib/jvm?

/opt/sun-jdk

Спасибо.

Кстати, Oracle:

Installation of Oracle Linux JDK using archive binaries (.tar.gz) allows you to install a private version of the JDK for the current user into any location, without affecting other JDK installations. However, it may involve manual steps to get some of the features to work (for example, the -version:release option of the java command which allows you to specify the release to be used to run the specified class requires the correct path to the JDK release under /usr/jdk).

Смотря для чего.

Для Qt, android (SDK, NDK) я использовал /usr/lib/jvm.