As mentioned in this thread, you can only do that (meaning "disabling the leading asterisks") by going to
Preferences > Java > Code Style > Code Templates
So for example, if you modify the template for comments of a field into:
/**
*/
It will come that way (without any asterisk in the middle) when you will comment a Field.
However, it does go against the Sun convention for Java comment formatting (as seen also here)...
An even simpler way (if you only need to do that for certain comments of your codes, while keeping the other one with the standard style) is, when a multi-line comment appear like this one:
/**
*
*/
, you can first remove the one leading asterisk, the enter your comments.
You will see no other leading asterisks are showing up at the beginning of each new line of comments.
/**
*/
/**
My first line of comment
My second line of comment
My third line of comment
*/