You can use wordcount that works with 7.1 nb-wordcount that works with 8.2.
To configure wordcount go in Tools->Options->Miscellaneous.
You have to change Accept filename if you want other files than Java and Groovy to match.
To display the count window go in Window->Open WordCount Window.
To display stats click on WordCounting (second button). I will display the stats of the directory selected in Projects (window)(it has to be a package or something like Source Packages or Web pages, it won’t work if you select the project).
Also if you are on linux you can simply execute :
find . -name '*.java' | xargs wc -l