I made the mistake of not taking into consideration of the API level of each method used in my code. So after coding 500 lines, I have no idea what is the highest Android API level I have used in my code.
Obviously, I hope I do not have to check through every single line of method for its API level so I am wondering is there an option in Eclipse to check the highest API level method which I had used.
Set your target SDK level to your minimum SDK, set your project build target to be the same API level, recompile and fix the errors as they show up.
Note that you will still have to handle API behavior changes like what happened with AsyncTask, but its a start.