java: fix some javadoc errors

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Change-Id: I09e090c6cc49366191f96d34bd51f6ba68cf18aa
Reviewed-on: https://gerrit.libreoffice.org/12524
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>