What does speech recognition have to do with JTextArea? Do you want to the recognized text to appear in one? That's easy to do, one you have accomplished speech recognition. Which, of course, is the hard part.
A Java Speech API has been defined by Sun -for both speech synthesization and recognition-, but those are interfaces only, not implementations. Speech recognition implementations in particular are few and far in between, see here. As this is a hard problem to do well, just about all of them are commercial.