There are really two separate warnings here. One is "unmappable character for encoding UTF8" and the other is the rest: "Some input files use unchecked or unsafe operations. Recompile with -Xlint:unchecked for details." Regarding the second one: This means that you are using a generic class without the generic type parameter. For example, the class ArrayList has a type parameter. You declare it as ArrayList<String> myList; or ArrayList<Enemies> allEnemies; You also use the type parameter when creating the object: myList = new ArrayList<String>(); Now, if you forget to use the type parameter and just write ArrayList instead of ArrayList<String>, then you will get the warning above. So look through your code for generic classes where you have forgotten the generic type.

Hi, I saw this message today: "unmappable character for encoding UTF8" I run greenfoot on ubuntu 11.04. It was a class that had some strange characters in a comment (this hapened because of changing computers, and i write in portuguese with accents). I fixed it and it executed as usual.