Try this regex to search replace either in eclipse / sed / your favorite editor that has regex support.
/**(?s:(?!*/).)**/
?s
treat input as single line
- a starting string
**
- zero or more
- negative lookahead for
*/
- space or non space char
- a trailing string
*/
Edit
To tackle cases where strings containing javadoc, use this regex
((?<!\)"([^"]|(?<=\)")*")|(/**(?s:(?!*/).)**/)
and replace it with first capture group
/1
Then if you say this shouldn't match
///** */
or more complex cases
I suggest, using a parser tool like antlr to parse using java grammar for tokens like comments and strings and remove elements that you don't want
Sometime I find my own regex answers cryptic !!
So here is some visual feedback
((?!\)"([^"]|(?=\)")*")|(/**(?:(?!*/).)**/)
Debuggex Demo
/**(?:(?!*/).)**/
Debuggex Demo
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