There is description of interned String in doc. of jmap -permstat.

http://docs.oracle.com/javase/7/docs/technotes/tools/share/jmap.html
| -permstat
| .......In addition, the number and size of interned Strings are printed.

However, the inf. of "the number and size of interned Strings." is not diplayed with -permstat, but with -heap.
The above-mentioned inf. should be moved to the description of "-heap" option.