I'm sorry, you must have misunderstood what I was saying. When I said recompile what I was saying was recompile it with the flag. That is
javac -Xlint:unchecked something.java
Where something.java is your code, etc.
I am also confused on one point in your code. You create a new ArrayList called coefficients in your constructor, but I don't see it as global, public, private, static, anything. So my question is how are you doing a set on it at all?