Without looking at the full code its hard to figure out exactly why.. but I'm guessing its because choices is not initiailised:

Try

private List choices = new ArrayList();

or

Before choices.add(choice); insert

if(choices == null) {

choices = new ArrayList();

}

Unless you need Java your best bet is to either uninstall it or turn it off. Java is a security nightmare.

Would like to see the implementation of Question class too. Because that is being inherited here!!

And the method setAnswer() belongs to that class!

remove "or"