I got downvotes on this question that I asked on Stack Overflow.
I don't understand why I got the downvotes and want to improve my question. Can anyone here please help me in this?
Your original question (before being edited by other user) was very unclear. Big part is because of bad English and grammar, unprofessional sentences like "and draw very slow ,yes ,sloooooow".
Another big issue is that you did not ask any real question. Title like "I develop a game use bluetooth in android" is also very bad: people see this and think "cool, so this person develop a game. So what?".
In short, your original question needed a big improvement. Now that it's edited and improved, it already got 3 upvotes and if those who downvoted will come back they might undo their vote as well.
If you can further improve that question please do it, for future questions take your time, read other questions on the android tag that got upvotes and think well before posting.