You have to modify your game code and port it into Java ME. Because Java ME has less methods than Java SE, you must modify some (may be many) on your code. for developing game you can use GameCanvas instead of Canvas, which supports more game functions (key control, sound, animation, etc). ngg... where should we start? I think Jason Lam (http://www.jasonlam604.com/books.php) has made a clear explanation and tutorial on how to make a Java mobile game. you can start from there.
subject: How do I create a game made using Java playable on mobile phones?